Nuclear charge radii: density functional theory meets Bayesian neural networks

NASA Astrophysics Data System (ADS)

Utama, R.; Chen, Wei-Chia; Piekarewicz, J.

2016-11-01

The distribution of electric charge in atomic nuclei is fundamental to our understanding of the complex nuclear dynamics and a quintessential observable to validate nuclear structure models. The aim of this study is to explore a novel approach that combines sophisticated models of nuclear structure with Bayesian neural networks (BNN) to generate predictions for the charge radii of thousands of nuclei throughout the nuclear chart. A class of relativistic energy density functionals is used to provide robust predictions for nuclear charge radii. In turn, these predictions are refined through Bayesian learning for a neural network that is trained using residuals between theoretical predictions and the experimental data. Although predictions obtained with density functional theory provide a fairly good description of experiment, our results show significant improvement (better than 40%) after BNN refinement. Moreover, these improved results for nuclear charge radii are supplemented with theoretical error bars. We have successfully demonstrated the ability of the BNN approach to significantly increase the accuracy of nuclear models in the predictions of nuclear charge radii. However, as many before us, we failed to uncover the underlying physics behind the intriguing behavior of charge radii along the calcium isotopic chain.

Structure and capacitance of an electric double layer of an asymmetric valency dimer electrolyte: A comparison of the density functional theory with Monte Carlo simulations

DOE PAGES

Henderson, Douglas; Silvestre-Alcantara, Whasington; Kaja, Monika; ...

2016-08-18

Here, the density functional theory is applied to a study of the structure and differential capacitance of a planar electric double layer formed by a valency asymmetric mixture of charged dimers and monomers. The dimer consists of two tangentially tethered hard spheres of equal diameters of which one is charged and the other is neutral, while the monomer is a charged hard sphere of the same size. The dimer electrolyte is next to a uniformly charged, smooth planar electrode. The electrode-particle singlet distributions, the mean electrostatic potential, and the differential capacitance for the model double layer are evaluated for amore » 2:1/1:2 valency electrolyte at a given concentration. Important consequences of asymmetry in charges and in ion shapes are (i) a finite, non-zero potential of zero charge, and (ii) asymmetric shaped 2:1 and 1:2 capacitance curves which are not mirror images of each other. Comparisons of the density functional results with the corresponding Monte Carlo simulations show the theoretical predictions to be in good agreement with the simulations overall except near zero surface charge.« less

Modelling charge transfer reactions with the frozen density embedding formalism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavanello, Michele; Neugebauer, Johannes

2011-12-21

The frozen density embedding (FDE) subsystem formulation of density-functional theory is a useful tool for studying charge transfer reactions. In this work charge-localized, diabatic states are generated directly with FDE and used to calculate electronic couplings of hole transfer reactions in two {pi}-stacked nucleobase dimers of B-DNA: 5{sup '}-GG-3{sup '} and 5{sup '}-GT-3{sup '}. The calculations rely on two assumptions: the two-state model, and a small differential overlap between donor and acceptor subsystem densities. The resulting electronic couplings agree well with benchmark values for those exchange-correlation functionals that contain a high percentage of exact exchange. Instead, when semilocal GGA functionalsmore » are used the electronic couplings are grossly overestimated.« less

Kapton charging characteristics: Effects of material thickness and electron-energy distribution

NASA Technical Reports Server (NTRS)

Williamson, W. S.; Dulgeroff, C. R.; Hymann, J.; Viswanathan, R.

1985-01-01

Charging characteristics of polyimide (Kapton) of varying thicknesses under irradiation by a very-low-curent-density electron beam, with the back surface of the sample grounded are reported. These charging characteristics are in good agreement with a simple analytical model which predicts that in thin samples at low current density, sample surface potential is limited by conduction leakage through the bulk material. The charging of Kapton in a low-current-density electron beam in which the beam energy was modulated to simulate Maxwellian and biMaxwellian distribution functions is measured.

Communication: Correct charge transfer in CT complexes from the Becke'05 density functional

NASA Astrophysics Data System (ADS)

Becke, Axel D.; Dale, Stephen G.; Johnson, Erin R.

2018-06-01

It has been known for over twenty years that density functionals of the generalized-gradient approximation (GGA) type and exact-exchange-GGA hybrids with low exact-exchange mixing fraction yield enormous errors in the properties of charge-transfer (CT) complexes. Manifestations of this error have also plagued computations of CT excitation energies. GGAs transfer far too much charge in CT complexes. This error has therefore come to be called "delocalization" error. It remains, to this day, a vexing unsolved problem in density-functional theory (DFT). Here we report that a 100% exact-exchange-based density functional known as Becke'05 or "B05" [A. D. Becke, J. Chem. Phys. 119, 2972 (2003); 122, 064101 (2005)] predicts excellent charge transfers in classic CT complexes involving the electron donors NH3, C2H4, HCN, and C2H2 and electron acceptors F2 and Cl2. Our approach is variational, as in our recent "B05min" dipole moments paper [Dale et al., J. Chem. Phys. 147, 154103 (2017)]. Therefore B05 is not only an accurate DFT for thermochemistry but is promising as a solution to the delocalization problem as well.

Adequate representation of charge polarization effects leads to a successful treatment of the CF4 + SiCl4 → CCl4 + SiF4 reaction by density functional theory.

PubMed

Li, Ruifang; Zhao, Yan; Truhlar, Donald G

2011-02-28

Adequate polarization functions reduce the error of density functional theory (DFT) for the heat of reaction for CF(4) + SiCl(4) from ∼9-12 kcal mol(-1) to ∼2-4 kcal mol(-1), and using an improved density functional further reduces it to ∼1 kcal mol(-1). This reaction was previously identified as a stumbling block for DFT, but we show that the problem with the previous calculations was not DFT but rather inadequate basis sets to account for intramolecular charge polarization.

Charge transport calculations by a wave-packet dynamical approach using maximally localized Wannier functions based on density functional theory: Application to high-mobility organic semiconductors

NASA Astrophysics Data System (ADS)

Ishii, Hiroyuki; Kobayashi, Nobuhiko; Hirose, Kenji

2017-01-01

We present a wave-packet dynamical approach to charge transport using maximally localized Wannier functions based on density functional theory including van der Waals interactions. We apply it to the transport properties of pentacene and rubrene single crystals and show the temperature-dependent natures from bandlike to thermally activated behaviors as a function of the magnitude of external static disorder. We compare the results with those obtained by the conventional band and hopping models and experiments.

Fractional Wigner Crystal in the Helical Luttinger Liquid.

PubMed

Traverso Ziani, N; Crépin, F; Trauzettel, B

2015-11-13

The properties of the strongly interacting edge states of two dimensional topological insulators in the presence of two-particle backscattering are investigated. We find an anomalous behavior of the density-density correlation functions, which show oscillations that are neither of Friedel nor of Wigner type: they, instead, represent a Wigner crystal of fermions of fractional charge e/2, with e the electron charge. By studying the Fermi operator, we demonstrate that the state characterized by such fractional oscillations still bears the signatures of spin-momentum locking. Finally, we compare the spin-spin correlation functions and the density-density correlation functions to argue that the fractional Wigner crystal is characterized by a nontrivial spin texture.

Gravity dual of spin and charge density waves

NASA Astrophysics Data System (ADS)

Jokela, Niko; Järvinen, Matti; Lippert, Matthew

2014-12-01

At high enough charge density, the homogeneous state of the D3-D7' model is unstable to fluctuations at nonzero momentum. We investigate the end point of this instability, finding a spatially modulated ground state, which is a charge and spin density wave. We analyze the phase structure of the model as a function of chemical potential and magnetic field and find the phase transition from the homogeneous state to be first order, with a second-order critical point at zero magnetic field.

Charge Transfer Enhancement in the D-π-A Type Porphyrin Dyes: A Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) Study.

PubMed

Kang, Guo-Jun; Song, Chao; Ren, Xue-Feng

2016-11-25

The electronic geometries and optical properties of two D-π-A type zinc porphyrin dyes (NCH₃-YD2 and TPhe-YD) were systematically investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to reveal the origin of significantly altered charge transfer enhancement by changing the electron donor of the famous porphyrin-based sensitizer YD2-o-C8. The molecular geometries and photophysical properties of dyes before and after binding to the TiO₂ cluster were fully investigated. From the analyses of natural bond orbital (NBO), extended charge decomposition analysis (ECDA), and electron density variations (Δρ) between the excited state and ground state, it was found that the introduction of N(CH₃)₂ and 1,1,2-triphenylethene groups enhanced the intramolecular charge-transfer (ICT) character compared to YD2-o-C8. The absorption wavelength and transition possess character were significantly influenced by N(CH₃)₂ and 1,1,2-triphenylethene groups. NCH₃-YD2 with N(CH₃)₂ groups in the donor part is an effective way to improve the interactions between the dyes and TiO₂ surface, light having efficiency (LHE), and free energy change (ΔG inject ), which is expected to be an efficient dye for use in dye-sensitized solar cells (DSSCs).

Modulating the fixed charge density in silicon nitride films while monitoring the surface recombination velocity by photoluminescence imaging

NASA Astrophysics Data System (ADS)

Bazilchuk, Molly; Haug, Halvard; Marstein, Erik Stensrud

2015-04-01

Several important semiconductor devices such as solar cells and photodetectors may be fabricated based on surface inversion layer junctions induced by fixed charge in a dielectric layer. Inversion layer junctions can easily be fabricated by depositing layers with a high density of fixed charge on a semiconducting substrate. Increasing the fixed charge improves such devices; for instance, the efficiency of a solar cell can be substantially increased by reducing the surface recombination velocity, which is a function of the fixed charge density. Methods for increasing the charge density are therefore of interest. In this work, the fixed charge density in silicon nitride layers deposited by plasma enhanced chemical vapor deposition is increased to very high values above 1 × 1013 cm-2 after the application of an external voltage to a gate electrode. The effect of the fixed charge density on the surface recombination velocity was experimentally observed using the combination of capacitance-voltage characterization and photoluminescence imaging, showing a significant reduction in the surface recombination velocity for increasing charge density. The surface recombination velocity vs. charge density data was analyzed using a numerical device model, which indicated the presence of a sub-surface damage region formed during deposition of the layers. Finally, we have demonstrated that the aluminum electrodes used for charge injection may be chemically removed in phosphoric acid without loss of the underlying charge. The injected charge was shown to be stable for a prolonged time period, leading us to propose charge injection in silicon nitride films by application of soaking voltage as a viable method for fabricating inversion layer devices.

Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

PubMed Central

Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

2016-01-01

Local surface charge density of lipid membranes influences membrane–protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values. PMID:27561322

Observation of a Charge Density Wave Incommensuration Near the Superconducting Dome in Cu x TiSe 2

DOE PAGES

Kogar, A.; de la Pena, G. A.; Lee, Sangjun; ...

2017-01-11

X-ray diffraction was employed to study the evolution of the charge density wave (CDW) in Cu xTiSe 2 as a function of copper intercalation in order to clarify the relationship between the CDW and superconductivity. In this paper, the results show a CDW incommensuration arising at an intercalation value coincident with the onset of superconductivity at around x = 0.055(5) . Additionally, it was found that the charge density wave persists to higher intercalant concentrations than previously assumed, demonstrating that the CDW does not terminate inside the superconducting dome. A charge density wave peak was observed in samples up tomore » x = 0.091(6) , the highest copper concentration examined in this study. Lastly, the phase diagram established in this work suggests that charge density wave incommensuration may play a role in the formation of the superconducting state.« less

Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

NASA Astrophysics Data System (ADS)

Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

2016-08-01

Local surface charge density of lipid membranes influences membrane-protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values.

Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy.

PubMed

Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

2016-08-26

Local surface charge density of lipid membranes influences membrane-protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values.

Time-dependent density functional theory for the charging kinetics of electric double layer containing room-temperature ionic liquids

DOE PAGES

Lian, Cheng; Univ. of California, Riverside, CA; Zhao, Shuangliang; ...

2016-11-29

Understanding the charging kinetics of electric double layers is of fundamental importance for the design and development of novel electrochemical devices such as supercapacitors and field-effect transistors. In this paper, we study the dynamic behavior of room-temperature ionic liquids using a classical time-dependent density functional theory that accounts for the molecular excluded volume effects, the electrostatic correlations, and the dispersion forces. While the conventional models predict a monotonic increase of the surface charge with time upon application of an electrode voltage, our results show that dispersion between ions results in a non-monotonic increase of the surface charge with the durationmore » of charging. Finally and furthermore, we investigate the effects of van der Waals attraction between electrode/ionic-liquid interactions on the charging processes.« less

Self-consistent calculations for the electronic structure of a vacancy in copper. A solution of the embedding problem

NASA Astrophysics Data System (ADS)

Zeller, R.; Braspenning, P. J.

1982-06-01

The charge density and the local density of states for a vacancy in Cu and for the first shell of Cu neighbours are calculated by the KKR-Green's function technique. The muffin-tin potentials for the vacancy and the neighbour shell atoms are determined self-consistently in the local density approximation of density functional theory. By the use of the proper host Green's function the embedding of this cluster of 13 perturbed muffin-tins into the infinite array of bulk Cu muffin-tin potentials is described rigorously, thus representing a solution of the embedding problem. The calculations demonstrate a rather large charge transfer of 1.1 electrons from the first neighbour shell to the vacancy.

Investigation of ground state charge transfer complex between paracetamol and p-chloranil through DFT and UV-visible studies

NASA Astrophysics Data System (ADS)

Shukla, Madhulata; Srivastava, Nitin; Saha, Satyen

2012-08-01

The present report deals with the theoretical investigation on ground state structure and charge transfer (CT) transitions in paracetamol (PA)/p-chloranil (CA) complex using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) method. It is found that Cdbnd O bond length of p-chloranil increases on complexation with paracetamol along with considerable amount of charge transfer from PA to CA. TD-DFT calculations have been performed to analyse the observed UV-visible spectrum of PA-CA charge transferred complex. Interestingly, in addition to expected CT transition, a weak symmetry relieved π-π* transition in the chloranil is also observed.

Quantum mechanical/molecular mechanical/continuum style solvation model: time-dependent density functional theory.

PubMed

Thellamurege, Nandun M; Cui, Fengchao; Li, Hui

2013-08-28

A combined quantum mechanical/molecular mechanical/continuum (QM/MMpol/C) style method is developed for time-dependent density functional theory (TDDFT, including long-range corrected TDDFT) method, induced dipole polarizable force field, and induced surface charge continuum model. Induced dipoles and induced charges are included in the TDDFT equations to solve for the transition energies, relaxed density, and transition density. Analytic gradient is derived and implemented for geometry optimization and molecular dynamics simulation. QM/MMpol/C style DFT and TDDFT methods are used to study the hydrogen bonding of the photoactive yellow protein chromopore in ground state and excited state.

Interaction potential for indium phosphide: a molecular dynamics and first-principles study of the elastic constants, generalized stacking fault and surface energies.

PubMed

Branicio, Paulo Sergio; Rino, José Pedro; Gan, Chee Kwan; Tsuzuki, Hélio

2009-03-04

Indium phosphide is investigated using molecular dynamics (MD) simulations and density-functional theory calculations. MD simulations use a proposed effective interaction potential for InP fitted to a selected experimental dataset of properties. The potential consists of two- and three-body terms that represent atomic-size effects, charge-charge, charge-dipole and dipole-dipole interactions as well as covalent bond bending and stretching. Predictions are made for the elastic constants as a function of density and temperature, the generalized stacking fault energy and the low-index surface energies.

Phosphorene quantum dot-fullerene nanocomposites for solar energy conversion: An unexplored inorganic-organic nanohybrid with novel photovoltaic properties

NASA Astrophysics Data System (ADS)

Rajbanshi, Biplab; Kar, Moumita; Sarkar, Pallavi; Sarkar, Pranab

2017-10-01

Using the self-consistent charge density-functional based tight-binding (SCC-DFTB) method, coupled with time-dependent density functional theory (TDDFT) calculations, for the first time we explore the possibility of use of phosphorene quantum dots in solar energy harvesting devices. The phosphorene quantum dots-fullerene (PQDs-PCBA) nanocomposites show type-II band alignment indicating spatial separation of charge carriers. The TDDFT calculations also show that the PQD-fullerene nanocomposites seem to be exciting material for future generation solar energy harvester, with extremely fast charge transfer and very poor recombination rate.

Insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor devices with Al2O3 or AlTiO gate dielectrics

NASA Astrophysics Data System (ADS)

Le, Son Phuong; Nguyen, Duong Dai; Suzuki, Toshi-kazu

2018-01-01

We have investigated insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor (MIS) devices with Al2O3 or AlTiO (an alloy of Al2O3 and TiO2) gate dielectrics obtained by atomic layer deposition on AlGaN. Analyzing insulator-thickness dependences of threshold voltages for the MIS devices, we evaluated positive interface fixed charges, whose density at the AlTiO/AlGaN interface is significantly lower than that at the Al2O3/AlGaN interface. This and a higher dielectric constant of AlTiO lead to rather shallower threshold voltages for the AlTiO gate dielectric than for Al2O3. The lower interface fixed charge density also leads to the fact that the two-dimensional electron concentration is a decreasing function of the insulator thickness for AlTiO, whereas being an increasing function for Al2O3. Moreover, we discuss the relationship between the interface fixed charges and interface states. From the conductance method, it is shown that the interface state densities are very similar at the Al2O3/AlGaN and AlTiO/AlGaN interfaces. Therefore, we consider that the lower AlTiO/AlGaN interface fixed charge density is not owing to electrons trapped at deep interface states compensating the positive fixed charges and can be attributed to a lower density of oxygen-related interface donors.

Holographic entanglement entropy of a 1 + 1 dimensional p-wave superconductor

NASA Astrophysics Data System (ADS)

Das, Sumit R.; Fujita, Mitsutoshi; Kim, Bom Soo

2017-09-01

We examine the behavior of entanglement entropy S A EE of a subsystem A in a fully backreacted holographic model of a 1 + 1 dimensional p wave superconductor across the phase transition. For a given temperature, the system goes to a superconducting phase beyond a critical value of the charge density. The entanglement entropy, considered as a function of the charge density at a given temperature, has a cusp at the critical point. In addition, we find that there are three different behaviors in the condensed phase, depending on the subsystem size. For a subsystem size l smaller than a critical size l c1, S A EE continues to increase as a function of the charge density as we cross the phase transition. When l lies between l c1 and another critical size l c2 the entanglement entropy displays a non-monotonic behavior, while for l > l c2 it decreases monotonically. At large charge densities S A EE appears to saturate. The non-monotonic behavior leads to a novel phase diagram for this system.

Density-based Energy Decomposition Analysis for Intermolecular Interactions with Variationally Determined Intermediate State Energies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Q.; Ayers, P.W.; Zhang, Y.

2009-10-28

The first purely density-based energy decomposition analysis (EDA) for intermolecular binding is developed within the density functional theory. The most important feature of this scheme is to variationally determine the frozen density energy, based on a constrained search formalism and implemented with the Wu-Yang algorithm [Q. Wu and W. Yang, J. Chem. Phys. 118, 2498 (2003) ]. This variational process dispenses with the Heitler-London antisymmetrization of wave functions used in most previous methods and calculates the electrostatic and Pauli repulsion energies together without any distortion of the frozen density, an important fact that enables a clean separation of these twomore » terms from the relaxation (i.e., polarization and charge transfer) terms. The new EDA also employs the constrained density functional theory approach [Q. Wu and T. Van Voorhis, Phys. Rev. A 72, 24502 (2005)] to separate out charge transfer effects. Because the charge transfer energy is based on the density flow in real space, it has a small basis set dependence. Applications of this decomposition to hydrogen bonding in the water dimer and the formamide dimer show that the frozen density energy dominates the binding in these systems, consistent with the noncovalent nature of the interactions. A more detailed examination reveals how the interplay of electrostatics and the Pauli repulsion determines the distance and angular dependence of these hydrogen bonds.« less

When combined X-ray and polarized neutron diffraction data challenge high-level calculations: spin-resolved electron density of an organic radical.

PubMed

Voufack, Ariste Bolivard; Claiser, Nicolas; Lecomte, Claude; Pillet, Sébastien; Pontillon, Yves; Gillon, Béatrice; Yan, Zeyin; Gillet, Jean Michel; Marazzi, Marco; Genoni, Alessandro; Souhassou, Mohamed

2017-08-01

Joint refinement of X-ray and polarized neutron diffraction data has been carried out in order to determine charge and spin density distributions simultaneously in the nitronyl nitroxide (NN) free radical Nit(SMe)Ph. For comparison purposes, density functional theory (DFT) and complete active-space self-consistent field (CASSCF) theoretical calculations were also performed. Experimentally derived charge and spin densities show significant differences between the two NO groups of the NN function that are not observed from DFT theoretical calculations. On the contrary, CASSCF calculations exhibit the same fine details as observed in spin-resolved joint refinement and a clear asymmetry between the two NO groups.

Application of double-hybrid density functionals to charge transfer in N-substituted pentacenequinones.

PubMed

Sancho-García, J C

2012-05-07

A set of N-heteroquinones, deriving from oligoacenes, have been recently proposed as n-type organic semiconductors with high electron mobilities in thin-film transistors. Generally speaking, this class of compounds self-assembles in neighboring π-stacks linked by weak hydrogen bonds. We aim at theoretically characterizing here the sequential charge transport (hopping) process expected to take place across these arrays of molecules. To do so, we need to accurately address the preferred packing of these materials simultaneously to single-molecule properties related to charge-transfer events, carefully employing dispersion-corrected density functional theory methods to accurately extract the key molecular parameters governing this phenomenon at the nanoscale. This study confirms the great deal of interest around these compounds, since controlled functionalization of model molecules (i.e., pentacene) allows to efficiently tune the corresponding charge mobilities, and the capacity of modern quantum-chemical methods to predict it after rationalizing the underlying structure-property relationships.

Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory.

PubMed

Sissay, Adonay; Abanador, Paul; Mauger, François; Gaarde, Mette; Schafer, Kenneth J; Lopata, Kenneth

2016-09-07

Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagating the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.

Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sissay, Adonay; Abanador, Paul; Mauger, François

2016-09-07

Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagatingmore » the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.« less

Novel Approach to Evaluation of Charging on Semiconductor Surface by Noncontact, Electrode-Free Capacitance/Voltage Measurement

NASA Astrophysics Data System (ADS)

Hirae, Sadao; Kohno, Motohiro; Okada, Hiroshi; Matsubara, Hideaki; Nakatani, Ikuyoshi; Kusuda, Tatsufumi; Sakai, Takamasa

1994-04-01

This paper describes a novel approach to the quantitative characterization of semiconductor surface charging caused by plasma exposures and ion implantations. The problems in conventional evaluation of charging are also discussed. Following the discussions above, the necessity of unified criteria is suggested for efficient development of systems or processes without charging damage. Hence, the charging saturation voltage between a top oxide surface and substrate, V s, and the charging density per unit area per second, ρ0, should be taken as criteria of charging behavior, which effectively represent the charging characteristics of both processes. The unified criteria can be obtained from the exposure time dependence of a net charging density on the thick field oxide. In order to determine V s and ρ0, the analysis using the C-V curve measured in a noncontact method with the metal-air-insulator-semiconductor (MAIS) technique is employed. The total space-charge density in oxide and its centroid can be determined at the same time by analyzing the flat-band voltage (V fb) of the MAIS capacitor as a function of the air gap. The net charge density can be obtained by analyzing the difference between the total space-charge density in oxide before and after charging. Finally, it is shown that charge damage of the large area metal-oxide-semiconductor (MOS) capacitor can be estimated from both V s and ρ0 which are obtained from results for a thick field oxide implanted with As+ and exposed to oxygen plasma.

Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions

DOE PAGES

Duignan, Timothy T.; Baer, Marcel D.; Schenter, Gregory K.; ...

2017-07-26

Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for models of electrolyte solution. In this paper, we provide definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation and isolate the effects of charge and cavitation, comparing tomore » the Born (linear response) model. We show that using uncorrected Ewald summation leads to unphysical values for the single ion solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small non-linearity for small anions. The charge hydration asymmetry for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. Finally, this suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation.« less

Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duignan, Timothy T.; Baer, Marcel D.; Schenter, Gregory K.

Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for models of electrolyte solution. In this paper, we provide definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation and isolate the effects of charge and cavitation, comparing tomore » the Born (linear response) model. We show that using uncorrected Ewald summation leads to unphysical values for the single ion solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small non-linearity for small anions. The charge hydration asymmetry for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. Finally, this suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation.« less

Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions

NASA Astrophysics Data System (ADS)

Duignan, Timothy T.; Baer, Marcel D.; Schenter, Gregory K.; Mundy, Chistopher J.

2017-10-01

Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for models of electrolyte solution. Here, we provide definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation and isolate the effects of charge and cavitation, comparing to the Born (linear response) model. We show that using uncorrected Ewald summation leads to unphysical values for the single ion solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small non-linearity for small anions. The charge hydration asymmetry for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. This suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation.

Scaling relations for a needle-like electron beam plasma from the self-similar behavior in beam propagation

NASA Astrophysics Data System (ADS)

Bai, Xiaoyan; Chen, Chen; Li, Hong; Liu, Wandong; Chen, Wei

2017-10-01

Scaling relations of the main parameters of a needle-like electron beam plasma (EBP) to the initial beam energy, beam current, and discharge pressures are presented. The relations characterize the main features of the plasma in three parameter space and can provide great convenience in plasma design with electron beams. First, starting from the self-similar behavior of electron beam propagation, energy and charge depositions in beam propagation were expressed analytically as functions of the three parameters. Second, according to the complete coupled theoretical model of an EBP and appropriate assumptions, independent equations controlling the density and space charges were derived. Analytical expressions for the density and charges versus functions of energy and charge depositions were obtained. Finally, with the combination of the expressions derived in the above two steps, scaling relations of the density and potential to the three parameters were constructed. Meanwhile, numerical simulations were used to test part of the scaling relations.

Electronic structure and partial charge distribution of Doxorubicin in different molecular environments.

PubMed

Poudel, Lokendra; Wen, Amy M; French, Roger H; Parsegian, V Adrian; Podgornik, Rudolf; Steinmetz, Nicole F; Ching, Wai-Yim

2015-05-18

The electronic structure and partial charge of doxorubicin (DOX) in three different molecular environments-isolated, solvated, and intercalated in a DNA complex-are studied by first-principles density functional methods. It is shown that the addition of solvating water molecules to DOX, together with the proximity to and interaction with DNA, has a significant impact on the electronic structure as well as on the partial charge distribution. Significant improvement in estimating the DOX-DNA interaction energy is achieved. The results are further elucidated by resolving the total density of states and surface charge density into different functional groups. It is concluded that the presence of the solvent and the details of the interaction geometry matter greatly in determining the stability of DOX complexation. Ab initio calculations on realistic models are an important step toward a more accurate description of the long-range interactions in biomolecular systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nonlocal and Nonadiabatic Effects in the Charge-Density Response of Solids: A Time-Dependent Density-Functional Approach

NASA Astrophysics Data System (ADS)

Panholzer, Martin; Gatti, Matteo; Reining, Lucia

2018-04-01

The charge-density response of extended materials is usually dominated by the collective oscillation of electrons, the plasmons. Beyond this feature, however, intriguing many-body effects are observed. They cannot be described by one of the most widely used approaches for the calculation of dielectric functions, which is time-dependent density functional theory (TDDFT) in the adiabatic local density approximation (ALDA). Here, we propose an approximation to the TDDFT exchange-correlation kernel which is nonadiabatic and nonlocal. It is extracted from correlated calculations in the homogeneous electron gas, where we have tabulated it for a wide range of wave vectors and frequencies. A simple mean density approximation allows one to use it in inhomogeneous materials where the density varies on a scale of 1.6 rs or faster. This kernel contains effects that are completely absent in the ALDA; in particular, it correctly describes the double plasmon in the dynamic structure factor of sodium, and it shows the characteristic low-energy peak that appears in systems with low electronic density. It also leads to an overall quantitative improvement of spectra.

Nonlocal and Nonadiabatic Effects in the Charge-Density Response of Solids: A Time-Dependent Density-Functional Approach.

PubMed

Panholzer, Martin; Gatti, Matteo; Reining, Lucia

2018-04-20

The charge-density response of extended materials is usually dominated by the collective oscillation of electrons, the plasmons. Beyond this feature, however, intriguing many-body effects are observed. They cannot be described by one of the most widely used approaches for the calculation of dielectric functions, which is time-dependent density functional theory (TDDFT) in the adiabatic local density approximation (ALDA). Here, we propose an approximation to the TDDFT exchange-correlation kernel which is nonadiabatic and nonlocal. It is extracted from correlated calculations in the homogeneous electron gas, where we have tabulated it for a wide range of wave vectors and frequencies. A simple mean density approximation allows one to use it in inhomogeneous materials where the density varies on a scale of 1.6 r_{s} or faster. This kernel contains effects that are completely absent in the ALDA; in particular, it correctly describes the double plasmon in the dynamic structure factor of sodium, and it shows the characteristic low-energy peak that appears in systems with low electronic density. It also leads to an overall quantitative improvement of spectra.

Charge transport in nanostructured materials: Implementation and verification of constrained density functional theory

DOE PAGES

Goldey, Matthew B.; Brawand, Nicholas P.; Voros, Marton; ...

2017-04-20

The in silico design of novel complex materials for energy conversion requires accurate, ab initio simulation of charge transport. In this work, we present an implementation of constrained density functional theory (CDFT) for the calculation of parameters for charge transport in the hopping regime. We verify our implementation against literature results for molecular systems, and we discuss the dependence of results on numerical parameters and the choice of localization potentials. In addition, we compare CDFT results with those of other commonly used methods for simulating charge transport between nanoscale building blocks. As a result, we show that some of thesemore » methods give unphysical results for thermally disordered configurations, while CDFT proves to be a viable and robust approach.« less

Theoretical models for electron conduction in polymer systems—I. Macroscopic calculations of d.c. transient conductivity after pulse irradiation

NASA Astrophysics Data System (ADS)

Bartczak, Witold M.; Kroh, Jerzy

The simulation of the transient d.c. conductivity in a quasi one-dimensional system of charges produced by a pulse of ionizing radiation in a solid sample has been performed. The simulation is based on the macroscopic conductivity equations and can provide physical insight into d.c. conductivity measurements, particularly for the case of transient currents in samples with internal space charge. We consider the system of mobile (negative) and immobile (positive) charges produced by a pulse of ionizing radiation in the sample under a fixed external voltage V0. The presence of space charge results in an electric field which is a function of both the spatial and the time variable: E( z, t). Given the space charge density, the electric field can be calculated from the Poisson equation. However, for an arbitrary space charge distribution, the corresponding equations can only be solved numerically. The two non-trivial cases for which approximate analytical solutions can be provided are: (i) The density of the current carriers n( z, t) is negligible in comparison with the density of immobile space charge N( z). A general analytical solution has been found for this case using Green's functions. The solutions for two cases, viz. the homogeneous distribution of space charge N( z) = N, and the non-homogeneous exponential distribution N( z) = A exp(- Bz), have been separately discussed. (ii) The space charge created in the pulse without any space charge present prior to the irradiation.

Electronic Coupling Calculations for Bridge-Mediated Charge Transfer Using Constrained Density Functional Theory (CDFT) and Effective Hamiltonian Approaches at the Density Functional Theory (DFT) and Fragment-Orbital Density Functional Tight Binding (FODFTB) Level

DOE PAGES

Gillet, Natacha; Berstis, Laura; Wu, Xiaojing; ...

2016-09-09

In this paper, four methods to calculate charge transfer integrals in the context of bridge-mediated electron transfer are tested. These methods are based on density functional theory (DFT). We consider two perturbative Green's function effective Hamiltonian methods (first, at the DFT level of theory, using localized molecular orbitals; second, applying a tight-binding DFT approach, using fragment orbitals) and two constrained DFT implementations with either plane-wave or local basis sets. To assess the performance of the methods for through-bond (TB)-dominated or through-space (TS)-dominated transfer, different sets of molecules are considered. For through-bond electron transfer (ET), several molecules that were originally synthesizedmore » by Paddon-Row and co-workers for the deduction of electronic coupling values from photoemission and electron transmission spectroscopies, are analyzed. The tested methodologies prove to be successful in reproducing experimental data, the exponential distance decay constant and the superbridge effects arising from interference among ET pathways. For through-space ET, dedicated p-stacked systems with heterocyclopentadiene molecules were created and analyzed on the basis of electronic coupling dependence on donor-acceptor distance, structure of the bridge, and ET barrier height. The inexpensive fragment-orbital density functional tight binding (FODFTB) method gives similar results to constrained density functional theory (CDFT) and both reproduce the expected exponential decay of the coupling with donor-acceptor distances and the number of bridging units. Finally, these four approaches appear to give reliable results for both TB and TS ET and present a good alternative to expensive ab initio methodologies for large systems involving long-range charge transfers.« less

Electronic Coupling Calculations for Bridge-Mediated Charge Transfer Using Constrained Density Functional Theory (CDFT) and Effective Hamiltonian Approaches at the Density Functional Theory (DFT) and Fragment-Orbital Density Functional Tight Binding (FODFTB) Level

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gillet, Natacha; Berstis, Laura; Wu, Xiaojing

In this paper, four methods to calculate charge transfer integrals in the context of bridge-mediated electron transfer are tested. These methods are based on density functional theory (DFT). We consider two perturbative Green's function effective Hamiltonian methods (first, at the DFT level of theory, using localized molecular orbitals; second, applying a tight-binding DFT approach, using fragment orbitals) and two constrained DFT implementations with either plane-wave or local basis sets. To assess the performance of the methods for through-bond (TB)-dominated or through-space (TS)-dominated transfer, different sets of molecules are considered. For through-bond electron transfer (ET), several molecules that were originally synthesizedmore » by Paddon-Row and co-workers for the deduction of electronic coupling values from photoemission and electron transmission spectroscopies, are analyzed. The tested methodologies prove to be successful in reproducing experimental data, the exponential distance decay constant and the superbridge effects arising from interference among ET pathways. For through-space ET, dedicated p-stacked systems with heterocyclopentadiene molecules were created and analyzed on the basis of electronic coupling dependence on donor-acceptor distance, structure of the bridge, and ET barrier height. The inexpensive fragment-orbital density functional tight binding (FODFTB) method gives similar results to constrained density functional theory (CDFT) and both reproduce the expected exponential decay of the coupling with donor-acceptor distances and the number of bridging units. Finally, these four approaches appear to give reliable results for both TB and TS ET and present a good alternative to expensive ab initio methodologies for large systems involving long-range charge transfers.« less

Electronic Coupling Calculations for Bridge-Mediated Charge Transfer Using Constrained Density Functional Theory (CDFT) and Effective Hamiltonian Approaches at the Density Functional Theory (DFT) and Fragment-Orbital Density Functional Tight Binding (FODFTB) Level.

PubMed

Gillet, Natacha; Berstis, Laura; Wu, Xiaojing; Gajdos, Fruzsina; Heck, Alexander; de la Lande, Aurélien; Blumberger, Jochen; Elstner, Marcus

2016-10-11

In this article, four methods to calculate charge transfer integrals in the context of bridge-mediated electron transfer are tested. These methods are based on density functional theory (DFT). We consider two perturbative Green's function effective Hamiltonian methods (first, at the DFT level of theory, using localized molecular orbitals; second, applying a tight-binding DFT approach, using fragment orbitals) and two constrained DFT implementations with either plane-wave or local basis sets. To assess the performance of the methods for through-bond (TB)-dominated or through-space (TS)-dominated transfer, different sets of molecules are considered. For through-bond electron transfer (ET), several molecules that were originally synthesized by Paddon-Row and co-workers for the deduction of electronic coupling values from photoemission and electron transmission spectroscopies, are analyzed. The tested methodologies prove to be successful in reproducing experimental data, the exponential distance decay constant and the superbridge effects arising from interference among ET pathways. For through-space ET, dedicated π-stacked systems with heterocyclopentadiene molecules were created and analyzed on the basis of electronic coupling dependence on donor-acceptor distance, structure of the bridge, and ET barrier height. The inexpensive fragment-orbital density functional tight binding (FODFTB) method gives similar results to constrained density functional theory (CDFT) and both reproduce the expected exponential decay of the coupling with donor-acceptor distances and the number of bridging units. These four approaches appear to give reliable results for both TB and TS ET and present a good alternative to expensive ab initio methodologies for large systems involving long-range charge transfers.

Efficiently accounting for ion correlations in electrokinetic nanofluidic devices using density functional theory.

PubMed

Gillespie, Dirk; Khair, Aditya S; Bardhan, Jaydeep P; Pennathur, Sumita

2011-07-15

The electrokinetic behavior of nanofluidic devices is dominated by the electrical double layers at the device walls. Therefore, accurate, predictive models of double layers are essential for device design and optimization. In this paper, we demonstrate that density functional theory (DFT) of electrolytes is an accurate and computationally efficient method for computing finite ion size effects and the resulting ion-ion correlations that are neglected in classical double layer theories such as Poisson-Boltzmann. Because DFT is derived from liquid-theory thermodynamic principles, it is ideal for nanofluidic systems with small spatial dimensions, high surface charge densities, high ion concentrations, and/or large ions. Ion-ion correlations are expected to be important in these regimes, leading to nonlinear phenomena such as charge inversion, wherein more counterions adsorb at the wall than is necessary to neutralize its surface charge, leading to a second layer of co-ions. We show that DFT, unlike other theories that do not include ion-ion correlations, can predict charge inversion and other nonlinear phenomena that lead to qualitatively different current densities and ion velocities for both pressure-driven and electro-osmotic flows. We therefore propose that DFT can be a valuable modeling and design tool for nanofluidic devices as they become smaller and more highly charged. Copyright © 2011 Elsevier Inc. All rights reserved.

Structure of an electric double layer containing a 2:2 valency dimer electrolyte

DOE PAGES

Silvestre-Alcantara, Whasington; Henderson, Douglas; Wu, Jianzhong; ...

2014-12-05

In this study, the structure of a planar electric double layer formed by a 2:2 valency dimer electrolyte in the vicinity of a uniformly charged planar hard electrode is investigated using density functional theory and Monte Carlo simulations. The dimer electrolyte consists of a mixture of charged divalent dimers and charged divalent monomers in a dielectric continuum. A dimer is constructed by two tangentially tethered rigid spheres, one of which is divalent and positively charged and the other neutral, whereas the monomer is a divalent and negatively charged rigid sphere. The density functional theory reproduces well the simulation results formore » (i) the singlet distributions of the various ion species with respect to the electrode, and (ii) the mean electrostatic potential. Lastly, comparison with earlier results for a 2:1/1:2 dimer electrolyte shows that the double layer structure is similar when the counterion has the same valency.« less

Poisson-Boltzmann theory of the charge-induced adsorption of semi-flexible polyelectrolytes.

PubMed

Ubbink, Job; Khokhlov, Alexei R

2004-03-15

A model is suggested for the structure of an adsorbed layer of a highly charged semi-flexible polyelectrolyte on a weakly charged surface of opposite charge sign. The adsorbed phase is thin, owing to the effective reversal of the charge sign of the surface upon adsorption, and ordered, owing to the high surface density of polyelectrolyte strands caused by the generally strong binding between polyelectrolyte and surface. The Poisson-Boltzmann equation for the electrostatic interaction between the array of adsorbed polyelectrolytes and the charged surface is solved for a cylindrical geometry, both numerically, using a finite element method, and analytically within the weak curvature limit under the assumption of excess monovalent salt. For small separations, repulsive surface polarization and counterion osmotic pressure effects dominate over the electrostatic attraction and the resulting electrostatic interaction curve shows a minimum at nonzero separations on the Angstrom scale. The equilibrium density of the adsorbed phase is obtained by minimizing the total free energy under the condition of equality of chemical potential and osmotic pressure of the polyelectrolyte in solution and in the adsorbed phase. For a wide range of ionic conditions and charge densities of the charged surface, the interstrand separation as predicted by the Poisson-Boltzmann model and the analytical theory closely agree. For low to moderate charge densities of the adsorbing surface, the interstrand spacing decreases as a function of the charge density of the charged surface. Above about 0.1 M excess monovalent salt, it is only weakly dependent on the ionic strength. At high charge densities of the adsorbing surface, the interstrand spacing increases with increasing ionic strength, in line with the experiments by Fang and Yang [J. Phys. Chem. B 101, 441 (1997)]. (c) 2004 American Institute of Physics.

Photoinduced charge-transfer electronic excitation of tetracyanoethylene/tetramethylethylene complex in dichloromethane

NASA Astrophysics Data System (ADS)

Xu, Long-Kun; Bi, Ting-Jun; Ming, Mei-Jun; Wang, Jing-Bo; Li, Xiang-Yuan

2017-07-01

Based on the previous work on nonequilibrium solvation model by the authors, Intermolecular charge-transfer electronic excitation of tetracyanoethylene (TCE)/tetramethylethylene (TME) π -stacked complex in dichloromethane (DCM) has been investigated. For weak interaction correction, dispersion corrected functional DFT-D3 is adopted for geometry optimization. In order to identify the excitation metric, dipole moment components of each Cartesian direction, atomic charge, charge separation and Δr index are analyzed for TCE/TME complex. Calculation shows that the calculated excitation energy is dependent on the functional choice, when conjuncted with suitable time-dependent density functional, the modified nonequilibrium expression gives satisfied results for intermolecular charge-transfer electronic excitation.

A hybrid density functional study of silicon and phosphorus doped hexagonal boron nitride monolayer

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Igumbor, E.; Chetty, N.

2016-10-01

We present a hybrid density functional study of silicon (Si) and phosphorus (P) doped hexagonal boron nitride (h-BN). The local geometry, electronic structure and thermodynamic stability of Si B , Si N , P B and P N are examined using hybrid Heyd-Scuseria- Ernzerhof (HSE) functional. The defect induced buckling and the local bond distances around the defect are sensitive to charge state modulation q = -2, -1, 0, +1 and +2. The +1 charge state is found to be the most energetically stable state and significantly reduces the buckling. Based on the charge state thermodynamic transition levels, we noted that the Si N , Si N and P B defects are too deep to be ionized, and can alter the optical properties of h-BN material.

C library for topological study of the electronic charge density.

PubMed

Vega, David; Aray, Yosslen; Rodríguez, Jesús

2012-12-05

The topological study of the electronic charge density is useful to obtain information about the kinds of bonds (ionic or covalent) and the atom charges on a molecule or crystal. For this study, it is necessary to calculate, at every space point, the electronic density and its electronic density derivatives values up to second order. In this work, a grid-based method for these calculations is described. The library, implemented for three dimensions, is based on a multidimensional Lagrange interpolation in a regular grid; by differentiating the resulting polynomial, the gradient vector, the Hessian matrix and the Laplacian formulas were obtained for every space point. More complex functions such as the Newton-Raphson method (to find the critical points, where the gradient is null) and the Cash-Karp Runge-Kutta method (used to make the gradient paths) were programmed. As in some crystals, the unit cell has angles different from 90°, the described library includes linear transformations to correct the gradient and Hessian when the grid is distorted (inclined). Functions were also developed to handle grid containing files (grd from DMol® program, CUBE from Gaussian® program and CHGCAR from VASP® program). Each one of these files contains the data for a molecular or crystal electronic property (such as charge density, spin density, electrostatic potential, and others) in a three-dimensional (3D) grid. The library can be adapted to make the topological study in any regular 3D grid by modifying the code of these functions. Copyright © 2012 Wiley Periodicals, Inc.

Time-dependent transition density matrix for visualizing charge-transfer excitations in photoexcited organic donor-acceptor systems

NASA Astrophysics Data System (ADS)

Li, Yonghui; Ullrich, Carsten

2013-03-01

The time-dependent transition density matrix (TDM) is a useful tool to visualize and interpret the induced charges and electron-hole coherences of excitonic processes in large molecules. Combined with time-dependent density functional theory on a real-space grid (as implemented in the octopus code), the TDM is a computationally viable visualization tool for optical excitation processes in molecules. It provides real-time maps of particles and holes which gives information on excitations, in particular those that have charge-transfer character, that cannot be obtained from the density alone. Some illustration of the TDM and comparison with standard density difference plots will be shown for photoexcited organic donor-acceptor molecules. This work is supported by NSF Grant DMR-1005651

Restoring the consistency with the contact density theorem of a classical density functional theory of ions at a planar electrical double layer.

PubMed

Gillespie, Dirk

2014-11-01

Classical density functional theory (DFT) of fluids is a fast and efficient theory to compute the structure of the electrical double layer in the primitive model of ions where ions are modeled as charged, hard spheres in a background dielectric. While the hard-core repulsive component of this ion-ion interaction can be accurately computed using well-established DFTs, the electrostatic component is less accurate. Moreover, many electrostatic functionals fail to satisfy a basic theorem, the contact density theorem, that relates the bulk pressure, surface charge, and ion densities at their distances of closest approach for ions in equilibrium at a smooth, hard, planar wall. One popular electrostatic functional that fails to satisfy the contact density theorem is a perturbation approach developed by Kierlik and Rosinberg [Phys. Rev. A 44, 5025 (1991)PLRAAN1050-294710.1103/PhysRevA.44.5025] and Rosenfeld [J. Chem. Phys. 98, 8126 (1993)JCPSA60021-960610.1063/1.464569], where the full free-energy functional is Taylor-expanded around a bulk (homogeneous) reference fluid. Here, it is shown that this functional fails to satisfy the contact density theorem because it also fails to satisfy the known low-density limit. When the functional is corrected to satisfy this limit, a corrected bulk pressure is derived and it is shown that with this pressure both the contact density theorem and the Gibbs adsorption theorem are satisfied.

Electrokinetic flow in a capillary with a charge-regulating surface polymer layer.

PubMed

Keh, Huan J; Ding, Jau M

2003-07-15

An analytical study of the steady electrokinetic flow in a long uniform capillary tube or slit is presented. The inside wall of the capillary is covered by a layer of adsorbed or covalently bound charge-regulating polymer in equilibrium with the ambient electrolyte solution. In this solvent-permeable and ion-penetrable surface polyelectrolyte layer, ionogenic functional groups and frictional segments are assumed to distribute at uniform densities. The electrical potential and space charge density distributions in the cross section of the capillary are obtained by solving the linearized Poisson-Boltzmann equation. The fluid velocity profile due to the application of an electric field and a pressure gradient through the capillary is obtained from the analytical solution of a modified Navier-Stokes/Brinkman equation. Explicit formulas for the electroosmotic velocity, the average fluid velocity and electric current density on the cross section, and the streaming potential in the capillary are also derived. The results demonstrate that the direction of the electroosmotic flow and the magnitudes of the fluid velocity and electric current density are dominated by the fixed charge density inside the surface polymer layer, which is determined by the regulation characteristics such as the dissociation equilibrium constants of the ionogenic functional groups in the surface layer and the concentration of the potential-determining ions in the bulk solution.

Plane wave density functional molecular dynamics study of exothermic reactions of Al/CuO thermites

NASA Astrophysics Data System (ADS)

Oloriegbe, Suleiman; Sewell, Thomas; Chen, Zhen; Jiang, Shan; Gan, Yong

2014-03-01

Exothermic reactions between nanosize aluminum (Al) and copper oxide (CuO) structures are of current interest because of their high reaction enthalpy and energy density which exceed those of traditional monomolecular energetic compounds such as TNT, RDX, and HMX. In this work, molecular dynamics simulations with forces obtained from plane wave density functional theory are used to investigate the atomic-scale and electronic processes that occur during the fast thermite reactions between Al and CuO nanostructures under adiabatic conditions. Aluminum surfaces in contact with O-exposed and Cu-exposed CuO surfaces are studied. Starting from initial temperature T = 800 K, we have observed: faster chemical reaction at the oxygen-rich interface during the initial 0.5 ps, linear temperature rise, and fast oxygen diffusion into the Al region with the rate 1.87 X 10-3 cm2/s. The density-derived electrostatic and chemical method is used to evaluate the net atomic charges and charge transfer during the important redox processes. High charge density around the oxygen-exposed interface may be responsible for the faster initial reactions at that interface. The overall reaction rate, determined using the time evolution of Cu-O charge orbital overlap population, is approximately first order.

Ionic fluids with r-6 pair interactions have power-law electrostatic screening

NASA Astrophysics Data System (ADS)

Kjellander, Roland; Forsberg, Björn

2005-06-01

The decay behaviour of radial distribution functions for large distances r is investigated for classical Coulomb fluids where the ions interact with an r-6 potential (e.g. a dispersion interaction) in addition to the Coulombic and the short-range repulsive potentials (e.g. a hard core). The pair distributions and the density-density (NN), charge-density (QN) and charge-charge (QQ) correlation functions are investigated analytically and by Monte Carlo simulations. It is found that the NN correlation function ultimately decays like r-6 for large r, just as it does for fluids of electroneutral particles interacting with an r-6 potential. The prefactor is proportional to the squared compressibility in both cases. The QN correlations decay in general like r-8 and the QQ correlations like r-10 in the ionic fluid. The average charge density around an ion decays generally like r-8 and the average electrostatic potential like r-6. This behaviour is in stark contrast to the decay behaviour for classical Coulomb fluids in the absence of the r-6 potential, where all these functions decay exponentially for large r. The power-law decays are, however, the same as for quantum Coulomb fluids. This indicates that the inclusion of the dispersion interaction as an effective r-6 interaction potential in classical systems yields the same decay behaviour for the pair correlations as in quantum ionic systems. An exceptional case is the completely symmetric binary electrolyte for which only the NN correlation has a power-law decay but not the QQ correlations. These features are shown by an analysis of the bridge function.

Efficient mixing scheme for self-consistent all-electron charge density

NASA Astrophysics Data System (ADS)

Shishidou, Tatsuya; Weinert, Michael

2015-03-01

In standard ab initio density-functional theory calculations, the charge density ρ is gradually updated using the ``input'' and ``output'' densities of the current and previous iteration steps. To accelerate the convergence, Pulay mixing has been widely used with great success. It expresses an ``optimal'' input density ρopt and its ``residual'' Ropt by a linear combination of the densities of the iteration sequences. In large-scale metallic systems, however, the long range nature of Coulomb interaction often causes the ``charge sloshing'' phenomenon and significantly impacts the convergence. Two treatments, represented in reciprocal space, are known to suppress the sloshing: (i) the inverse Kerker metric for Pulay optimization and (ii) Kerker-type preconditioning in mixing Ropt. In all-electron methods, where the charge density does not have a converging Fourier representation, treatments equivalent or similar to (i) and (ii) have not been described so far. In this work, we show that, by going through the calculation of Hartree potential, one can accomplish the procedures (i) and (ii) without entering the reciprocal space. Test calculations are done with a FLAPW method.

Density functional description of size-dependent effects at nucleation on neutral and charged nanoparticles

NASA Astrophysics Data System (ADS)

Shchekin, Alexander K.; Lebedeva, Tatiana S.

2017-03-01

A numerical study of size-dependent effects in the thermodynamics of a small droplet formed around a solid nanoparticle has been performed within the square-gradient density functional theory. The Lennard-Jones fluid with the Carnahan-Starling model for the hard-sphere contribution to intermolecular interaction in liquid and vapor phases and interfaces has been used for description of the condensate. The intermolecular forces between the solid core and condensate molecules have been taken into account with the help of the Lennard-Jones part of the total molecular potential of the core. The influence of the electric charge of the particle has been considered under assumption of the central Coulomb potential in the medium with dielectric permittivity depending on local condensate density. The condensate density profiles and equimolecular radii for equilibrium droplets at different values of the condensate chemical potential have been computed in the cases of an uncharged solid core with the molecular potential, a charged core without molecular potential, and a core with joint action of the Coulomb and molecular potentials. The appearance of stable equilibrium droplets even in the absence of the electric charge has been commented. As a next step, the capillary, disjoining pressure, and electrostatic contributions to the condensate chemical potential have been considered and compared with the predictions of classical thermodynamics in a wide range of values of the droplet and the particle equimolecular radii. With the help of the found dependence of the condensate chemical potential in droplet on the droplet size, the activation barrier for nucleation on uncharged and charged particles has been computed as a function of the vapor supersaturation. Finally, the work of droplet formation and the work of wetting the particle have been found as functions of the droplet size.

Analysis of polarization in hydrogen bonded complexes: An asymptotic projection approach

NASA Astrophysics Data System (ADS)

Drici, Nedjoua

2018-03-01

The asymptotic projection technique is used to investigate the polarization effect that arises from the interaction between the relaxed, and frozen monomeric charge densities of a set of neutral and charged hydrogen bonded complexes. The AP technique based on the resolution of the original Kohn-Sham equations can give an acceptable qualitative description of the polarization effect in neutral complexes. The significant overlap of the electron densities, in charged and π-conjugated complexes, impose further development of a new functional, describing the coupling between constrained and non-constrained electron densities within the AP technique to provide an accurate representation of the polarization effect.

Effect of current density on electron beam induced charging in MgO

NASA Astrophysics Data System (ADS)

Boughariou, Aicha; Hachicha, Olfa; Kallel, Ali; Blaise, Guy

2005-11-01

It is well known that the presence of space charge in an insulator is correlated with an electric breakdown. Many studies have been carried out on the experimental characterization of space charges. In this paper, we outline the dependence on the current density of the charge-trapping phenomenon in magnesium oxide. Our study was performed with a dedicated scanning electron microscope (SEM) on the electrical property evolution of surface of magnesium oxide (1 0 0) (MgO) single crystal, during a 1.1, 5 and 30 keV electron irradiation. The types of charges trapped on the irradiated areas and the charging kinetics are determined by measuring the total secondary electron emission (SEE) σ during the injection process by means of two complementary detectors. At low energies 1.1 and 5 keV, two different kinds of self-regulated regime (σ = 1) were observed as a function of current density. At 30 keV energy, the electron emission appears to be stimulated by the current density, due to the Poole-Frenkel effect.

Investigating the topological structure of quenched lattice QCD with overlap fermions using a multi-probing approximation

NASA Astrophysics Data System (ADS)

Zou, You-Hao; Zhang, Jian-Bo; Xiong, Guang-Yi; Chen, Ying; Liu, Chuan; Liu, Yu-Bin; Ma, Jian-Ping

2017-10-01

The topological charge density and topological susceptibility are determined by a multi-probing approximation using overlap fermions in quenched SU(3) gauge theory. Then we investigate the topological structure of the quenched QCD vacuum, and compare it with results from the all-scale topological density. The results are consistent. Random permuted topological charge density is used to check whether these structures represent underlying ordered properties. The pseudoscalar glueball mass is extracted from the two-point correlation function of the topological charge density. We study 3 ensembles of different lattice spacing a with the same lattice volume 163×32. The results are compatible with the results of all-scale topological charge density, and the topological structures revealed by multi-probing are much closer to all-scale topological charge density than those from eigenmode expansion. Supported by National Natural Science Foundation of China (NSFC) (11335001, 11275169, 11075167), It is also supported in part by the DFG and the NSFC (11261130311) through funds provided to the Sino-German CRC 110 "Symmetries and the Emergence of Structure in QCD". This work was also funded in part by National Basic Research Program of China (973 Program) (2015CB856700)

Effect of Thermospheric Neutral Density upon Inner Trapped-belt Proton Flux

NASA Technical Reports Server (NTRS)

Wilson, Thomas L.; Lodhi, M. A. K.; Diaz, Abel B.

2007-01-01

We wish to point out that a secular change in the Earth's atmospheric neutral density alters charged-particle lifetime in the inner trapped radiation belts, in addition to the changes recently reported as produced by greenhouse gases. Heretofore, changes in neutral density have been of interest primarily because of their effect on the orbital drag of satellites. We extend this to include the orbital lifetime of charged particles in the lower radiation belts. It is known that the charged-belt population is coupled to the neutral density of the atmosphere through changes induced by solar activity, an effect produced by multiple scattering off neutral and ionized atoms along with ionization loss in the thermosphere where charged and neutral populations interact. It will be shown here that trapped-belt flux J is bivariant in energy E and thermospheric neutral density , as J(E,rho). One can conclude that proton lifetimes in these belts are also directly affected by secular changes in the neutral species populating the Earth s thermosphere. This result is a consequence of an intrinsic property of charged-particle flux, that flux is not merely a function of E but is dependent upon density rho when a background of neutrals is present.

A Density Functional Study of Atomic Hydrogen and Oxygen Chemisorptions on the (0001) Surface of Double Hexagonal Close Packed Americium

NASA Astrophysics Data System (ADS)

Dholabhai, Pratik; Atta-Fynn, Raymond; Ray, Asok

2008-03-01

Ab initio total energy calculations within the framework of density functional theory have been performed for atomic hydrogen and oxygen chemisorptions on the (0001) surface of double hexagonal packed americium using a full-potential all-electron linearized augmented plane wave plus local orbitals (FLAPW+lo) method. The three-fold hollow hcp site was found to be the most stable site for H adsorption, while the two-fold bridge adsorption site was found to be the most stable site for O adsorption. Chemisorption energies and adsorption geometries for different adsorption sites will be discussed. The change in work functions, magnetic moments, partial charges inside muffin-tins, difference charge density distributions and density of states for the bare Am slab and the Am slab after adsorption of the adatom will be discussed. The implications of chemisorption on Am 5f electron localization-delocalization will also be discussed.

A theoretical-electron-density databank using a model of real and virtual spherical atoms.

PubMed

Nassour, Ayoub; Domagala, Slawomir; Guillot, Benoit; Leduc, Theo; Lecomte, Claude; Jelsch, Christian

2017-08-01

A database describing the electron density of common chemical groups using combinations of real and virtual spherical atoms is proposed, as an alternative to the multipolar atom modelling of the molecular charge density. Theoretical structure factors were computed from periodic density functional theory calculations on 38 crystal structures of small molecules and the charge density was subsequently refined using a density model based on real spherical atoms and additional dummy charges on the covalent bonds and on electron lone-pair sites. The electron-density parameters of real and dummy atoms present in a similar chemical environment were averaged on all the molecules studied to build a database of transferable spherical atoms. Compared with the now-popular databases of transferable multipolar parameters, the spherical charge modelling needs fewer parameters to describe the molecular electron density and can be more easily incorporated in molecular modelling software for the computation of electrostatic properties. The construction method of the database is described. In order to analyse to what extent this modelling method can be used to derive meaningful molecular properties, it has been applied to the urea molecule and to biotin/streptavidin, a protein/ligand complex.

Collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model

DOE PAGES

Ulybyshev, Maksim; Winterowd, Christopher; Zafeiropoulos, Savvas

2017-11-09

Here in this article, we discuss the nontrivial collective charge excitations (plasmons) of the extended square lattice Hubbard model. Using a fully nonperturbative approach, we employ the hybrid Monte Carlo algorithm to simulate the system at half-filling. A modified Backus-Gilbert method is introduced to obtain the spectral functions via numerical analytic continuation. We directly compute the single-particle density of states which demonstrates the formation of Hubbard bands in the strongly correlated phase. The momentum-resolved charge susceptibility also is computed on the basis of the Euclidean charge-density-density correlator. In agreement with previous extended dynamical mean-field theory studies, we find that, atmore » high strength of the electron-electron interaction, the plasmon dispersion develops two branches.« less

Collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulybyshev, Maksim; Winterowd, Christopher; Zafeiropoulos, Savvas

Here in this article, we discuss the nontrivial collective charge excitations (plasmons) of the extended square lattice Hubbard model. Using a fully nonperturbative approach, we employ the hybrid Monte Carlo algorithm to simulate the system at half-filling. A modified Backus-Gilbert method is introduced to obtain the spectral functions via numerical analytic continuation. We directly compute the single-particle density of states which demonstrates the formation of Hubbard bands in the strongly correlated phase. The momentum-resolved charge susceptibility also is computed on the basis of the Euclidean charge-density-density correlator. In agreement with previous extended dynamical mean-field theory studies, we find that, atmore » high strength of the electron-electron interaction, the plasmon dispersion develops two branches.« less

Ab initio computation of the transition temperature of the charge density wave transition in TiS e2

NASA Astrophysics Data System (ADS)

Duong, Dinh Loc; Burghard, Marko; Schön, J. Christian

2015-12-01

We present a density functional perturbation theory approach to estimate the transition temperature of the charge density wave transition of TiS e2 . The softening of the phonon mode at the L point where in TiS e2 a giant Kohn anomaly occurs, and the energy difference between the normal and distorted phase are analyzed. Both features are studied as functions of the electronic temperature, which corresponds to the Fermi-Dirac distribution smearing value in the calculation. The transition temperature is found to be 500 and 600 K by phonon and energy analysis, respectively, in reasonable agreement with the experimental value of 200 K.

Evaluation of physics-based numerical modelling for diverse design architecture of perovskite solar cells

NASA Astrophysics Data System (ADS)

Mishra, A. K.; Catalan, Jorge; Camacho, Diana; Martinez, Miguel; Hodges, D.

2017-08-01

Solution processed organic-inorganic metal halide perovskite based solar cells are emerging as a new cost effective photovoltaic technology. In the context of increasing the power conversion efficiency (PCE) and sustainability of perovskite solar cells (PSC) devices, we comprehensively analyzed a physics-based numerical modelling for doped and un-doped PSC devices. Our analytics emphasized the role of different charge carrier layers from the view point of interfacial adhesion and its influence on charge extraction rate and charge recombination mechanism. Morphological and charge transport properties of perovskite thin film as a function of device architecture are also considered to investigate the photovoltaic properties of PSC. We observed that photocurrent is dominantly influenced by interfacial recombination process and photovoltage has functional relationship with defect density of perovskite absorption layer. A novel contour mapping method to understand the characteristics of current density-voltage (J-V) curves for each device as a function of perovskite layer thickness provide an important insight about the distribution spectrum of photovoltaic properties. Functional relationship of device efficiency and fill factor with absorption layer thickness are also discussed.

Communication: a density functional with accurate fractional-charge and fractional-spin behaviour for s-electrons.

PubMed

Johnson, Erin R; Contreras-García, Julia

2011-08-28

We develop a new density-functional approach combining physical insight from chemical structure with treatment of multi-reference character by real-space modeling of the exchange-correlation hole. We are able to recover, for the first time, correct fractional-charge and fractional-spin behaviour for atoms of groups 1 and 2. Based on Becke's non-dynamical correlation functional [A. D. Becke, J. Chem. Phys. 119, 2972 (2003)] and explicitly accounting for core-valence separation and pairing effects, this method is able to accurately describe dissociation and strong correlation in s-shell many-electron systems. © 2011 American Institute of Physics

Spacecraft Charging in Low Temperature Environments

NASA Technical Reports Server (NTRS)

Parker, Linda N.

2007-01-01

Spacecraft charging in plasma and radiation environments is a temperature dependent phenomenon due to the reduction of electrical conductivity in dielectric materials at low temperatures. Charging time constants are proportional to l/conductivity may become very large (on the order of days to years) at low temperatures and accumulation of charge densities in insulators in charging environments traditionally considered benign at ambient temperatures may be sufficient to produce charge densities and electric fields of concern in insulators at low temperatures. Low temperature charging is of interest because a number of spacecraft-primarily infrared astronomy and microwave cosmology observatories-are currently being design, built, and or operated at very cold temperatures on the order of 40K to 100K. This paper reviews the temperature dependence of spacecraft charging processes and material parameters important to charging as a function of temperature with an emphasis on low temperatures regimes.

Charge and Spin Dynamics of the Hubbard Chains

NASA Technical Reports Server (NTRS)

Park, Youngho; Liang, Shoudan

1999-01-01

We calculate the local correlation functions of charge and spin for the one-chain and two-chain Hubbard model using density matrix renormalization group method and the recursion technique. Keeping only finite number of states we get good accuracy for the low energy excitations. We study the charge and spin gaps, bandwidths and weights of the spectra for various values of the on-site Coulomb interaction U and the electron filling. In the low energy part, the local correlation functions are different for the charge and spin. The bandwidths are proportional to t for the charge and J for the spin respectively.

Charge and Spin Currents in Open-Shell Molecules:  A Unified Description of NMR and EPR Observables.

PubMed

Soncini, Alessandro

2007-11-01

The theory of EPR hyperfine coupling tensors and NMR nuclear magnetic shielding tensors of open-shell molecules in the limit of vanishing spin-orbit coupling (e.g., for organic radicals) is analyzed in terms of spin and charge current density vector fields. The ab initio calculation of the spin and charge current density response has been implemented at the Restricted Open-Shell Hartree-Fock, Unrestricted Hartree-Fock, and unrestricted GGA-DFT level of theory. On the basis of this formalism, we introduce the definition of nuclear hyperfine coupling density, a scalar function of position providing a partition of the EPR observable over the molecular domain. Ab initio maps of spin and charge current density and hyperfine coupling density for small radicals are presented and discussed in order to illustrate the interpretative advantages of the newly introduced approach. Recent NMR experiments providing evidence for the existence of diatropic ring currents in the open-shell singlet pancake-bonded dimer of the neutral phenalenyl radical are directly assessed via the visualization of the induced current density.

Spectral function from Reduced Density Matrix Functional Theory

NASA Astrophysics Data System (ADS)

Romaniello, Pina; di Sabatino, Stefano; Berger, Jan A.; Reining, Lucia

2015-03-01

In this work we focus on the calculation of the spectral function, which determines, for example, photoemission spectra, from reduced density matrix functional theory. Starting from its definition in terms of the one-body Green's function we derive an expression for the spectral function that depends on the natural occupation numbers and on an effective energy which accounts for all the charged excitations. This effective energy depends on the two-body as well as higher-order density matrices. Various approximations to this expression are explored by using the exactly solvable Hubbard chains.

First quantitative measurements of charged-particle stopping and its dependence on electron temperature and density in Inertial-Confinement-Fusion plasmas

NASA Astrophysics Data System (ADS)

Frenje, J.; Li, C. K.; Séguin, F.; Zylstra, A.; Rinderknecht, H.; Petrasso, R.; Delettrez, J.; Glebov, V.; Sangster, T.

2013-10-01

We report on the first quantitative measurements of charged-particle stopping in Inertial-Confinement-Fusion (ICF) plasmas at various conditions. In these experiments, four charged fusion products from the DD and D3He reactions in D3He gas-filled filled implosions were used to determine the stopping power of ICF plasmas at electron temperatures (Te) , ion temperatures (Ti) , and areal densities (ρR) in the range of 0.6-4.0 keV, 3-14 keV and 2-10 mg/cm2, respectively. The resulting data, in the form of measured energy downshift of the charged fusion products, clearly indicate that the stopping-power function depends strongly on Te. It was also observed that the stopping-power function change in characteristics for higher-density implosions in which ions and electrons equilibrate faster, resulting in higher Te relative to Ti and higher ρR s. These results will be modelled by Landau-Spitzer theory and contrasted to different stopping-power models. This work was partially supported by the US DOE, NLUF, LLE, and GA.

Charged dopants in neutral supercells through substitutional donor (acceptor): nitrogen donor charging of the nitrogen-vacancy center in diamond

NASA Astrophysics Data System (ADS)

Löfgren, Robin; Pawar, Ravinder; Öberg, Sven; Larsson, J. Andreas

2018-02-01

Charged defects are traditionally computed by adding (subtracting) electrons for negative (positive) impurities. When using periodic boundary conditions this results in artificially charged supercells that also require a compensating background charge of the opposite sign, which makes slab supercells problematic because of an arbitrary dependence on the vacuum thickness. In this work, we test the method of using neutral supercells through the use of a substitutional electron donor (acceptor) to describe charged systems. We use density functional theory (DFT) to compare the effects of charging the well-studied NV-center in diamond by a substitutional donor nitrogen. We investigate the influence of the donor-N on the NV-center properties as a function of the distance between them, and find that they converge toward those obtained when adding an electron. We analyze the spin density and conclude that the donor-N has a zero magnetic moment, and thus, will not be seen in electron spin resonance. We validate our DFT energies through comparison to GW simulations. Charging the NV-center with a substitutional donor-N enables accurate calculations of slabs, without the ambiguity of using charged supercells. Implantation of donor-N atoms opens up the possibility to engineer NV-centers with the desired charge state for future ICT and sensor applications.

Theoretical studies of the work functions of Pd-based bimetallic surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ding, Zhao-Bin; Wu, Feng; Wang, Yue-Chao

2015-06-07

Work functions of Pd-based bimetallic surfaces, including mainly M/Pd(111), Pd/M, and Pd/M/Pd(111) (M = 4d transition metals, Cu, Au, and Pt), are studied using density functional theory. We find that the work function of these bimetallic surfaces is significantly different from that of parent metals. Careful analysis based on Bader charges and electron density difference indicates that the variation of the work function in bimetallic surfaces can be mainly attributed to two factors: (1) charge transfer between the two different metals as a result of their different intrinsic electronegativity, and (2) the charge redistribution induced by chemical bonding between themore » top two layers. The first factor can be related to the contact potential, i.e., the work function difference between two metals in direct contact, and the second factor can be well characterized by the change in the charge spilling out into vacuum. We also find that the variation in the work functions of Pd/M/Pd(111) surfaces correlates very well with the variation of the d-band center of the surface Pd atom. The findings in this work can be used to provide general guidelines to design new bimetallic surfaces with desired electronic properties.« less

Multi-charge-state molecular dynamics and self-diffusion coefficient in the warm dense matter regime

NASA Astrophysics Data System (ADS)

Fu, Yongsheng; Hou, Yong; Kang, Dongdong; Gao, Cheng; Jin, Fengtao; Yuan, Jianmin

2018-01-01

We present a multi-ion molecular dynamics (MIMD) simulation and apply it to calculating the self-diffusion coefficients of ions with different charge-states in the warm dense matter (WDM) regime. First, the method is used for the self-consistent calculation of electron structures of different charge-state ions in the ion sphere, with the ion-sphere radii being determined by the plasma density and the ion charges. The ionic fraction is then obtained by solving the Saha equation, taking account of interactions among different charge-state ions in the system, and ion-ion pair potentials are computed using the modified Gordon-Kim method in the framework of temperature-dependent density functional theory on the basis of the electron structures. Finally, MIMD is used to calculate ionic self-diffusion coefficients from the velocity correlation function according to the Green-Kubo relation. A comparison with the results of the average-atom model shows that different statistical processes will influence the ionic diffusion coefficient in the WDM regime.

Elimination of Spurious Fractional Charges in Dissociating Molecules by Correcting the Shape of Approximate Kohn-Sham Potentials.

PubMed

Komsa, Darya N; Staroverov, Viktor N

2016-11-08

Standard density-functional approximations often incorrectly predict that heteronuclear diatomic molecules dissociate into fractionally charged atoms. We demonstrate that these spurious charges can be eliminated by adapting the shape-correction method for Kohn-Sham potentials that was originally introduced to improve Rydberg excitation energies [ Phys. Rev. Lett. 2012 , 108 , 253005 ]. Specifically, we show that if a suitably determined fraction of electron charge is added to or removed from a frontier Kohn-Sham orbital level, the approximate Kohn-Sham potential of a stretched molecule self-corrects by developing a semblance of step structure; if this potential is used to obtain the electron density of the neutral molecule, charge delocalization is blocked and spurious fractional charges disappear beyond a certain internuclear distance.

Dissociation and recombination of positive holes in minerals

NASA Technical Reports Server (NTRS)

Freund, Friedemann; Batllo, Francois; Freund, Minoru M.

1990-01-01

The formation mechanisms are described of positive holes - electronic defects in the O2 sublattice - with attention given to detecting the positive surface charge of minerals with these holes. Charge distribution analysis (CDA) is presented which measures dielectric polarization in an inhomogeneous field. CDA can be applied to the detection of the peroxide/superoxide functionality caused by positive holes on the surface. It is demonstrated with obsidian that the measurements provide data on O(-) mobility as a function of surface-charge carrier density and on O(-) generation as a function of temperature.

Oxygen vacancy diffusion in bulk SrTiO3 from density functional theory calculations

DOE PAGES

Zhang, Lipeng; Liu, Bin; Zhuang, Houlong; ...

2016-04-01

Point defects and point defect diffusion contribute significantly to the properties of perovskite materials. However, even for the prototypical case of oxygen vacancies in SrTiO 3 (STO), predictions vary widely. Here we present a comprehensive and systematic study of the diffusion barriers for this material. We use density functional theory (DFT) and assess the role of different cell sizes, density functionals, and charge states. Our results show that vacancy-induced octahedral rotations, which are limited by the boundary conditions of the supercell, can significantly affect the computed oxygen vacancy diffusion energy barrier. The diffusion energy barrier of a charged oxygen vacancymore » is lower than that of a neutral one. Unexpectedly, we find that with increasing supercell size, the effects of the oxygen vacancy charge state, the type of DFT exchange and correlation functional on the energy barrier diminish, and the different DFT predictions asymptote to a value in the range of 0.39-0.49 eV. This work provides important insight and guidance that should be considered for investigations of point defect diffusion in other perovskite materials and in oxide superlattices.« less

Determination of Charge-Carrier Mobility in Disordered Thin-Film Solar Cells as a Function of Current Density

NASA Astrophysics Data System (ADS)

Mäckel, Helmut; MacKenzie, Roderick C. I.

2018-03-01

Charge-carrier mobility is a fundamental material parameter, which plays an important role in determining solar-cell efficiency. The higher the mobility, the less time a charge carrier will spend in a device and the less likely it is that it will be lost to recombination. Despite the importance of this physical property, it is notoriously difficult to measure accurately in disordered thin-film solar cells under operating conditions. We, therefore, investigate a method previously proposed in the literature for the determination of mobility as a function of current density. The method is based on a simple analytical model that relates the mobility to carrier density and transport resistance. By revising the theoretical background of the method, we clearly demonstrate what type of mobility can be extracted (constant mobility or effective mobility of electrons and holes). We generalize the method to any combination of measurements that is able to determine the mean electron and hole carrier density, and the transport resistance at a given current density. We explore the robustness of the method by simulating typical organic solar-cell structures with a variety of physical properties, including unbalanced mobilities, unbalanced carrier densities, and for high or low carrier trapping rates. The simulations reveal that near VOC and JSC , the method fails due to the limitation of determining the transport resistance. However, away from these regions (and, importantly, around the maximum power point), the method can accurately determine charge-carrier mobility. In the presence of strong carrier trapping, the method overestimates the effective mobility due to an underestimation of the carrier density.

Electronic properties of B and Al doped graphane: A hybrid density functional study

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Igumbor, E.; Andriambelaza, N. F.; Chetty, N.

2018-04-01

Using a hybrid density functional theory approach parametrized by Heyd, Scuseria and Ernzerhof (HSE06 hybrid functional), we study the energetics, structural and electronic properties of a graphane monolayer substitutionally doped with the B (BCH) and Al (AlCH) atoms. The BCH defect can be integrated within a graphane monolayer at a relative low formation energy, without major structural distortions and symmetry breaking. The AlCH defect relaxes outward of the monolayer and breaks the symmetry. The density of states plots indicate that BCH doped graphane monolayer is a wide band gap semiconductor, whereas the AlCH defect introduces the spin dependent mid gap states at the vicinity of the Fermi level, revealing a metallic character with the pronounced magnetic features. We further examine the response of the Al dependent spin states on the multiple charge states doping. We find that the defect formation energy, structural and electronic properties can be altered via charge state modulation. The +1 charge doping opens an energy band gap of 1.75 eV. This value corresponds to the wavelength in the visible spectrum, suggesting an ideal material for solar cell absorbers. Our study fine tunes the graphane band gap through the foreign atom doping as well as via defect charge state modulation.

Theoretical analysis of the electronic properties of the sex pheromone and its analogue derivatives in the female processionary moth Thaumetopoea pytiocampa.

PubMed

Chamorro, Ester R; Sequeira, Alfredo F; Zalazar, M Fernanda; Peruchena, Nélida M

2008-09-15

In the present work, the distribution of the electronic charge density of the natural sex pheromone, the (Z)-13-hexadecen-11-ynyl acetate, in the female processionary moth, Thaumetopoea pytiocampa, and its nine analogue derivatives was studied within the framework of the Density Functional Theory and the Atoms in Molecules (AIM) Theory at B3LYP/6-31G *//B3LYP/6-31++G * * level. Additionally, molecular electrostatic potential (MEP) maps of the previously mentioned compounds were computed and compared. Furthermore, the substitution of hydrogen atoms from the methyl group in the acetate group by electron withdrawing substituents (i.e., halogen atoms) as well as the replacement effect of hydrogen by electron donor substituents (+I effect) as methyl group, were explored. The key feature of the topological distribution of the charge density in analogue compounds, such as the variations of the topological properties encountered in the region formed by neighbouring atoms from the substitution site were presented and discussed. Using topological parameters, such as electronic charge density, Laplacian, kinetic energy density, and potential energy density evaluated at bond critical points (BCP), we provide here a detailed analysis of the nature of the chemical bonding of these molecules. In addition, the atomic properties (population, charge, energy, volume, and dipole moment) were determined on selected atoms. These properties were analyzed at the substitution site (with respect to the natural sex pheromone) and related to the biological activity and to the possible binding site with the pheromone binding protein, (PBP). Moreover, the Laplacian function of the electronic density was used to locate electrophilic regions susceptible to be attacked (by deficient electron atoms or donor hydrogen). Our results indicate that the change in the atomic properties, such as electronic population and atomic volume, are sensitive indicators of the loss of the biological activity in the analogues studied here. The crucial interaction between the acetate group of the natural sex pheromone and the PBP is most likely to be a hydrogen bonding and the substitution of hydrogen atoms by electronegative atoms in the pheromone molecule reduces the hydrogen acceptor capacity. This situation is mirrored by the diminish of the electronic population on carbon and oxygen atoms at the carbonylic group in the halo-acetate group. Additionally, the modified acetate group (with electronegative atoms) shows new charge concentration critical points or regions of concentration of charge density in which an electrophilic attack can also occur. Finally, the use of the topological analysis based in the charge density distribution and its Laplacian function, in conjunction with MEP maps provides valuable information about the steric volume and electronic requirement of the sex pheromone for binding to the PBP.

Evaluation of reduced point charge models of proteins through Molecular Dynamics simulations: application to the Vps27 UIM-1-Ubiquitin complex.

PubMed

Leherte, Laurence; Vercauteren, Daniel P

2014-02-01

Reduced point charge models of amino acids are designed, (i) from local extrema positions in charge density distribution functions built from the Poisson equation applied to smoothed molecular electrostatic potential (MEP) functions, and (ii) from local maxima positions in promolecular electron density distribution functions. Corresponding charge values are fitted versus all-atom Amber99 MEPs. To easily generate reduced point charge models for protein structures, libraries of amino acid templates are built. The program GROMACS is used to generate stable Molecular Dynamics trajectories of an Ubiquitin-ligand complex (PDB: 1Q0W), under various implementation schemes, solvation, and temperature conditions. Point charges that are not located on atoms are considered as virtual sites with a nul mass and radius. The results illustrate how the intra- and inter-molecular H-bond interactions are affected by the degree of reduction of the point charge models and give directions for their implementation; a special attention to the atoms selected to locate the virtual sites and to the Coulomb-14 interactions is needed. Results obtained at various temperatures suggest that the use of reduced point charge models allows to probe local potential hyper-surface minima that are similar to the all-atom ones, but are characterized by lower energy barriers. It enables to generate various conformations of the protein complex more rapidly than the all-atom point charge representation. Copyright © 2013 Elsevier Inc. All rights reserved.

Polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent counterions: A Monte Carlo simulation study

NASA Astrophysics Data System (ADS)

Luque-Caballero, Germán; Martín-Molina, Alberto; Quesada-Pérez, Manuel

2014-05-01

Both experiments and theory have evidenced that multivalent cations can mediate the interaction between negatively charged polyelectrolytes and like-charged objects, such as anionic lipoplexes (DNA-cation-anionic liposome complexes). In this paper, we use Monte Carlo simulations to study the electrostatic interaction responsible for the trivalent-counterion-mediated adsorption of polyelectrolytes onto a like-charged planar surface. The evaluation of the Helmholtz free energy allows us to characterize both the magnitude and the range of the interaction as a function of the polyelectrolyte charge, surface charge density, [3:1] electrolyte concentration, and cation size. Both polyelectrolyte and surface charge favor the adsorption. It should be stressed, however, that the adsorption will be negligible if the surface charge density does not exceed a threshold value. The effect of the [3:1] electrolyte concentration has also been analyzed. In certain range of concentrations, the counterion-mediated attraction seems to be independent of this parameter, whereas very high concentrations of salt weaken the adsorption. If the trivalent cation diameter is doubled the adsorption moderates due to the excluded volume effects. The analysis of the integrated charge density and ionic distributions suggests that a delicate balance between charge inversion and screening effects governs the polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent cations.

Effects of Acids, Bases, and Heteroatoms on Proximal Radial Distribution Functions for Proteins.

PubMed

Nguyen, Bao Linh; Pettitt, B Montgomery

2015-04-14

The proximal distribution of water around proteins is a convenient method of quantifying solvation. We consider the effect of charged and sulfur-containing amino acid side-chain atoms on the proximal radial distribution function (pRDF) of water molecules around proteins using side-chain analogs. The pRDF represents the relative probability of finding any solvent molecule at a distance from the closest or surface perpendicular protein atom. We consider the near-neighbor distribution. Previously, pRDFs were shown to be universal descriptors of the water molecules around C, N, and O atom types across hundreds of globular proteins. Using averaged pRDFs, a solvent density around any globular protein can be reconstructed with controllable relative error. Solvent reconstruction using the additional information from charged amino acid side-chain atom types from both small models and protein averages reveals the effects of surface charge distribution on solvent density and improves the reconstruction errors relative to simulation. Solvent density reconstructions from the small-molecule models are as effective and less computationally demanding than reconstructions from full macromolecular models in reproducing preferred hydration sites and solvent density fluctuations.

Composite space charge density functions for the calculation of gamma sensitivity of self-powered neutron detectors, using Warren's model

NASA Astrophysics Data System (ADS)

Mahant, A. K.; Rao, P. S.; Misra, S. C.

1994-07-01

In the calculational model developed by Warren and Shah for the computation of the gamma sensitivity ( Sγ) it has been observed that the computed Sγ value is quite sensitive to the space charge distribution function assumed for the insulator region and the energy of the gamma photons. The Sγ of SPNDs with Pt, Co and V emitters (manufactured by Thermocoax, France) has been measured at 60Co photon energy and a good correlation between the measured and computed values has been obtained using a composite space charge density function (CSCD), the details of which are presented in this paper. The arguments are extended for evaluating the Sγ values of several SPNDs for which Warren and Shah reported the measured values for a prompt fission gamma spectrum obtained in a swimming pool reactor. These results are also discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsieh, AG; Bhadra, S; Hertzberg, BJ

We demonstrate that a simple acoustic time-of-flight experiment can measure the state of charge and state of health of almost any closed battery. An acoustic conservation law model describing the state of charge of a standard battery is proposed, and experimental acoustic results verify the simulated trends; furthermore, a framework relating changes in sound speed, via density and modulus changes, to state of charge and state of health within a battery is discussed. Regardless of the chemistry, the distribution of density within a battery must change as a function of state of charge and, along with density, the bulk modulimore » of the anode and cathode changes as well. The shifts in density and modulus also change the acoustic attenuation in a battery. Experimental results indicating both state-of-charge determination and irreversible physical changes are presented for two of the most ubiquitous batteries in the world, the lithium-ion 18650 and the alkaline LR6 (AA). Overall, a one-or two-point acoustic measurement can be related to the interaction of a pressure wave at multiple discrete interfaces within a battery, which in turn provides insights into state of charge, state of health, and mechanical evolution/degradation.« less

Describing long-range charge-separation processes with subsystem density-functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solovyeva, Alisa; Neugebauer, Johannes, E-mail: j.neugebauer@uni-muenster.de; Pavanello, Michele, E-mail: m.pavanello@rutgers.edu

2014-04-28

Long-range charge-transfer processes in extended systems are difficult to describe with quantum chemical methods. In particular, cost-effective (non-hybrid) approximations within time-dependent density functional theory (DFT) are not applicable unless special precautions are taken. Here, we show that the efficient subsystem DFT can be employed as a constrained DFT variant to describe the energetics of long-range charge-separation processes. A formal analysis of the energy components in subsystem DFT for such excitation energies is presented, which demonstrates that both the distance dependence and the long-range limit are correctly described. In addition, electronic couplings for these processes as needed for rate constants inmore » Marcus theory can be obtained from this method. It is shown that the electronic structure of charge-separated states constructed by a positively charged subsystem interacting with a negatively charged one is difficult to converge — charge leaking from the negative subsystem to the positive one can occur. This problem is related to the delocalization error in DFT and can be overcome with asymptotically correct exchange–correlation (XC) potentials or XC potentials including a sufficiently large amount of exact exchange. We also outline an approximate way to obtain charge-transfer couplings between locally excited and charge-separated states.« less

Electron-beam-charged dielectrics: Internal charge distribution

NASA Technical Reports Server (NTRS)

Beers, B. L.; Pine, V. W.

1981-01-01

Theoretical calculations of an electron transport model of the charging of dielectrics due to electron bombardment are compared to measurements of internal charge distributions. The emphasis is on the distribution of Teflon. The position of the charge centroid as a function of time is not monotonic. It first moves deeper into the material and then moves back near to the surface. In most time regimes of interest, the charge distribution is not unimodal, but instead has two peaks. The location of the centroid near saturation is a function of the incident current density. While the qualitative comparison of theory and experiment are reasonable, quantitative comparison shows discrepancies of as much as a factor of two.

Donation and back-donation analyzed through a charge transfer model based on density functional theory.

PubMed

Orozco-Valencia, Ulises; Gázquez, José L; Vela, Alberto

2017-07-01

The net charge transfer process that occurs between two species, A and B, interacting with each other, may be decomposed into two processes: one in which A receives charge from B, which can be identified as the electrophilic channel for A or the nucleophilic channel for B, and a second in which A donates charge to B, which can be identified as the nucleophilic channel for A or the electrophilic channel for B. By determining the amount of charge associated with both processes through the minimization of the interaction energy associated with each case, the expressions for the amount of charge involved in each case can be expressed in terms of the directional chemical potentials and the hardnesses of the interacting species. The correlation between the charges obtained for the interaction between phosphine ligands of the type PRR'R'' and Ni, and the A 1 carbonyl stretching frequency provides support for their interpretation as measures of the electrophilicity and nucleophilicity of a chemical species, and, at the same time, allows one to describe the donation and back-donation processes in terms of the density functional theory of chemical reactivity.

Injection-modulated polarity conversion by charge carrier density control via a self-assembled monolayer for all-solution-processed organic field-effect transistors

NASA Astrophysics Data System (ADS)

Roh, Jeongkyun; Lee, Taesoo; Kang, Chan-Mo; Kwak, Jeonghun; Lang, Philippe; Horowitz, Gilles; Kim, Hyeok; Lee, Changhee

2017-04-01

We demonstrated modulation of charge carrier densities in all-solution-processed organic field-effect transistors (OFETs) by modifying the injection properties with self-assembled monolayers (SAMs). The all-solution-processed OFETs based on an n-type polymer with inkjet-printed Ag electrodes were fabricated as a test platform, and the injection properties were modified by the SAMs. Two types of SAMs with different dipole direction, thiophenol (TP) and pentafluorobenzene thiol (PFBT) were employed, modifying the work function of the inkjet-printed Ag (4.9 eV) to 4.66 eV and 5.24 eV with TP and PFBT treatments, respectively. The charge carrier densities were controlled by the SAM treatment in both dominant and non-dominant carrier-channel regimes. This work demonstrates that control of the charge carrier densities can be efficiently achieved by modifying the injection property with SAM treatment; thus, this approach can achieve polarity conversion of the OFETs.

Reply to ``Comment on `Spin- and charge-ordering in oxygen-vacancy-ordered mixed-valence Sr4Fe4O11 ' ''

NASA Astrophysics Data System (ADS)

Ravindran, P.; Vidya, R.; Fjellvåg, H.; Kjekshus, A.

2008-04-01

Recently, using density-functional theoretical calculations, we have reported [Phys. Rev. B 74, 054422 (2006)] that formal Fe3+ ions reside at the square-pyramidal site and Fe4+ ions in the octahedral site in Sr4Fe4O11 . Based on the interpretation of experimental structural and Mössbauer data from the literature, Adler concludes that our previous first-principles results disagree with experiments on the assignment of oxidation states to Fe in the square-pyramidal and octahedral environments in Sr4Fe4O11 . From a critical examination of the structure data for Sr4Fe4O11 and related oxides with Fe in different oxidation states and theoretically simulated Mössbauer parameters (hyperfine field, isomer shift, and quadrupole splitting), here we show that information on charges residing on the different constituents cannot be directly derived either from experimental structure or Mössbauer data. From additional analyses of the chemical bonding on the basis of charge density, charge transfer, electron localization function, crystal orbital Hamilton population, Born effective charge, and partial density of states, we substantiate our previous assignment of formal Fe3+ and Fe4+ to the square-pyramidal and octahedral sites, respectively, in Sr4Fe4O11 .

Effective charges of ionic liquid determined self-consistently through combination of molecular dynamics simulation and density-functional theory.

PubMed

Ishizuka, Ryosuke; Matubayasi, Nobuyuki

2017-11-15

A self-consistent scheme combining the molecular dynamics (MD) simulation and density functional theory (DFT) was recently proposed to incorporate the effects of the charge transfer and polarization of ions into non-poralizable force fields of ionic liquids for improved description of energetics and dynamics. The purpose of the present work is to analyze the detailed setups of the MD/DFT scheme by focusing on how the basis set, exchange-correlation (XC) functional, charge-fitting method or force field for the intramolecular and Lennard-Jones interactions affects the MD/DFT results of 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide ( [C1mim][NTf2]) and 1-ethyl-3-methylimidazolium glycinate ( [C2mim][Gly]). It was found that the double-zeta valence polarized or larger size of basis set is required for the convergence of the effective charge of the ion. The choice of the XC functional was further not influential as far as the generalized gradient approximation is used. The charge-fitting method and force field govern the accuracy of the MD/DFT scheme, on the other hand. We examined the charge-fitting methods of Blöchl, the iterative Hirshfeld (Hirshfeld-I), and REPEAT in combination with Lopes et al.'s force field and general AMBER force field. There is no single combination of charge fitting and force field that provides good agreements with the experiments, while the MD/DFT scheme reduces the effective charges of the ions and leads to better description of energetics and dynamics compared to the original force field with unit charges. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Systematic Approach to Electrostatically Induced 2D Crystallization of Nanoparticles at Liquid Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukuto, M.; Kewalramani, S.; Wang, S.

2011-02-07

We report an experimental demonstration of a strategy for inducing two-dimensional (2D) crystallization of charged nanoparticles on oppositely charged fluid interfaces. This strategy aims to maximize the interfacial adsorption of nanoparticles, and hence their lateral packing density, by utilizing a combination of weakly charged particles and a high surface charge density on the planar interface. In order to test this approach, we investigated the assembly of cowpea mosaic virus (CPMV) on positively charged lipid monolayers at the aqueous solution surface, by means of in situ X-ray scattering measurements at the liquid-vapor interface. The assembly was studied as a function ofmore » the solution pH, which was used to vary the charge on CPMV, and of the mole fraction of the cationic lipid in the binary lipid monolayer, which set the interface charge density. The 2D crystallization of CPMV occurred in a narrow pH range just above the particle's isoelectric point, where the particle charge was weakly negative, and only when the cationic-lipid fraction in the monolayer exceeded a threshold. The observed 2D crystals exhibited nearly the same packing density as the densest lattice plane within the known 3D crystals of CPMV. The above electrostatic approach of maximizing interfacial adsorption may provide an efficient route to the crystallization of nanoparticles at aqueous interfaces.« less

Ion-mediated interactions in suspensions of oppositely charged nanoparticles

NASA Astrophysics Data System (ADS)

Dahirel, Vincent; Hansen, Jean Pierre

2009-08-01

The structure of oppositely charged spherical nanoparticles (polyions), dispersed in ionic solutions with continuous solvent (primitive model), is investigated by Monte Carlo (MC) simulations, within explicit and implicit microion representations, over a range of polyion valences and densities, and microion concentrations. Systems with explicit microions are explored by semigrand canonical MC simulations, and allow density-dependent effective polyion pair potentials vαβeff(r ) to be extracted from measured partial pair distribution functions. Implicit microion MC simulations are based on pair potentials of mean force vαβ(2)(r ) computed by explicit microion simulations of two charged polyions, in the low density limit. In the vicinity of the liquid-gas separation expected for oppositely charged polyions, the implicit microion representation leads to an instability against density fluctuations for polyion valences |Z| significantly below those at which the instability sets in within the exact explicit microion representation. Far from this instability region, the vαβ(2)(r ) are found to be fairly close to but consistently more repulsive than the effective pair potentials vαβeff(r ). This is corroborated by additional calculations of three-body forces between polyion triplets, which are repulsive when one polyion is of opposite charge to the other two. The explicit microion MC data were exploited to determine the ratio of salt concentrations c and co within the dispersion and the reservoir (Donnan effect). c /co is found to first increase before finally decreasing as a function of the polyion packing fraction.

Bulk and interfacial structures of reline deep eutectic solvent: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Kaur, Supreet; Sharma, Shobha; Kashyap, Hemant K.

2017-11-01

We apply all-atom molecular dynamics simulations to describe the bulk morphology and interfacial structure of reline, a deep eutectic solvent comprising choline chloride and urea in 1:2 molar ratio, near neutral and charged graphene electrodes. For the bulk phase structural investigation, we analyze the simulated real-space radial distribution functions, X-ray/neutron scattering structure functions, and their partial components. Our study shows that both hydrogen-bonding and long-range correlations between different constituents of reline play a crucial role to lay out the bulk structure of reline. Further, we examine the variation of number density profiles, orientational order parameters, and electrostatic potentials near the neutral and charged graphene electrodes with varying electrode charge density. The present study reveals the presence of profound structural layering of not only the ionic components of reline but also urea near the electrodes. In addition, depending on the electrode charge density, the choline ions and urea molecules render different orientations near the electrodes. The simulated number density and electrostatic potential profiles for reline clearly show the presence of multilayer structures up to a distance of 1.2 nm from the respective electrodes. The observation of positive values of the surface potential at zero charge indicates the presence of significant nonelectrostatic attraction between the choline cation and graphene electrode. The computed differential capacitance (Cd) for reline exhibits an asymmetric bell-shaped curve, signifying different variation of Cd with positive and negative surface potentials.

Bulk and interfacial structures of reline deep eutectic solvent: A molecular dynamics study.

PubMed

Kaur, Supreet; Sharma, Shobha; Kashyap, Hemant K

2017-11-21

We apply all-atom molecular dynamics simulations to describe the bulk morphology and interfacial structure of reline, a deep eutectic solvent comprising choline chloride and urea in 1:2 molar ratio, near neutral and charged graphene electrodes. For the bulk phase structural investigation, we analyze the simulated real-space radial distribution functions, X-ray/neutron scattering structure functions, and their partial components. Our study shows that both hydrogen-bonding and long-range correlations between different constituents of reline play a crucial role to lay out the bulk structure of reline. Further, we examine the variation of number density profiles, orientational order parameters, and electrostatic potentials near the neutral and charged graphene electrodes with varying electrode charge density. The present study reveals the presence of profound structural layering of not only the ionic components of reline but also urea near the electrodes. In addition, depending on the electrode charge density, the choline ions and urea molecules render different orientations near the electrodes. The simulated number density and electrostatic potential profiles for reline clearly show the presence of multilayer structures up to a distance of 1.2 nm from the respective electrodes. The observation of positive values of the surface potential at zero charge indicates the presence of significant nonelectrostatic attraction between the choline cation and graphene electrode. The computed differential capacitance (C d ) for reline exhibits an asymmetric bell-shaped curve, signifying different variation of C d with positive and negative surface potentials.

Possibility of transforming the electronic structure of one species of graphene adatoms into that of another by application of gate voltage: First-principles calculations

NASA Astrophysics Data System (ADS)

Chan, Kevin T.; Lee, Hoonkyung; Cohen, Marvin L.

2011-10-01

Graphene provides many advantages for controlling the electronic structure of adatoms and other adsorbates via gating. Using the projected density of states and charge density obtained from first-principles density-functional periodic supercell calculations, we investigate the possibility of performing “alchemy” of adatoms on graphene, i.e., transforming the electronic structure of one species of adatom into that of another species by application of a gate voltage. Gating is modeled as a change in the number of electrons in the unit cell, with the inclusion of a compensating uniform background charge. Within this model and the generalized gradient approximation to the exchange-correlation functional, we find that such transformations are possible for K, Ca, and several transition-metal adatoms. Gate control of the occupation of the p states of In on graphene is also investigated. The validity of the supercell approximation with uniform compensating charge and the model for exchange and correlation is also discussed.

Electron correlation and the self-interaction error of density functional theory

NASA Astrophysics Data System (ADS)

Polo, Victor; Kraka, Elfi; Cremer, Dieter

The self-interaction error (SIE) of commonly used DFT functionals has been systematically investigated by comparing the electron density distribution ρ( r ) generated by self-interaction corrected DFT (SIC-DFT) with a series of reference densities obtained by DFT or wavefunction theory (WFT) methods that cover typical electron correlation effects. Although the SIE of GGA functionals is considerably smaller than that of LDA functionals, it has significant consequences for the coverage of electron correlation effects at the DFT level of theory. The exchange SIE mimics long range (non-dynamic) pair correlation effects, and is responsible for the fact that the electron density of DFT exchange-only calculations resembles often that of MP4, MP2 or even CCSD(T) calculations. Changes in the electron density caused by SICDFT exchange are comparable with those that are associated with HF exchange. Correlation functionals contract the density towards the bond and the valence region, thus taking negative charge out of the van der Waals region where these effects are exaggerated by the influence of the SIE of the correlation functional. Hence, SIC-DFT leads in total to a relatively strong redistribution of negative charge from van der Waals, non-bonding, and valence regions of heavy atoms to the bond regions. These changes, although much stronger, resemble those obtained when comparing the densities of hybrid functionals such as B3LYP with the corresponding GGA functional BLYP. Hence, the balanced mixing of local and non-local exchange and correlation effects as it is achieved by hybrid functionals mimics SIC-DFT and can be considered as an economic way to include some SIC into standard DFT. However, the investigation shows also that the SIC-DFT description of molecules is unreliable because the standard functionals used were optimized for DFT including the SIE.

Estimate of size distribution of charged MSPs measured in situ in winter during the WADIS-2 sounding rocket campaign

NASA Astrophysics Data System (ADS)

Asmus, Heiner; Staszak, Tristan; Strelnikov, Boris; Lübken, Franz-Josef; Friedrich, Martin; Rapp, Markus

2017-08-01

We present results of in situ measurements of mesosphere-lower thermosphere dusty-plasma densities including electrons, positive ions and charged aerosols conducted during the WADIS-2 sounding rocket campaign. The neutral air density was also measured, allowing for robust derivation of turbulence energy dissipation rates. A unique feature of these measurements is that they were done in a true common volume and with high spatial resolution. This allows for a reliable derivation of mean sizes and a size distribution function for the charged meteor smoke particles (MSPs). The mean particle radius derived from Schmidt numbers obtained from electron density fluctuations was ˜ 0.56 nm. We assumed a lognormal size distribution of the charged meteor smoke particles and derived the distribution width of 1.66 based on in situ-measured densities of different plasma constituents. We found that layers of enhanced meteor smoke particles' density measured by the particle detector coincide with enhanced Schmidt numbers obtained from the electron and neutral density fluctuations. Thus, we found that large particles with sizes > 1 nm were stratified in layers of ˜ 1 km thickness and lying some kilometers apart from each other.

Communication: Hilbert-space partitioning of the molecular one-electron density matrix with orthogonal projectors

NASA Astrophysics Data System (ADS)

Vanfleteren, Diederik; Van Neck, Dimitri; Bultinck, Patrick; Ayers, Paul W.; Waroquier, Michel

2010-12-01

A double-atom partitioning of the molecular one-electron density matrix is used to describe atoms and bonds. All calculations are performed in Hilbert space. The concept of atomic weight functions (familiar from Hirshfeld analysis of the electron density) is extended to atomic weight matrices. These are constructed to be orthogonal projection operators on atomic subspaces, which has significant advantages in the interpretation of the bond contributions. In close analogy to the iterative Hirshfeld procedure, self-consistency is built in at the level of atomic charges and occupancies. The method is applied to a test set of about 67 molecules, representing various types of chemical binding. A close correlation is observed between the atomic charges and the Hirshfeld-I atomic charges.

Measurements of Ionospheric Density, Temperature, and Spacecraft Charging in a Space Weather Constellation

NASA Astrophysics Data System (ADS)

Balthazor, R. L.; McHarg, M. G.; Wilson, G.

2016-12-01

The Integrated Miniaturized Electrostatic Analyzer (IMESA) is a space weather sensor developed by the United States Air Force Academy and integrated and flown by the DoD's Space Test Program. IMESA records plasma spectrograms from which can be derived plasma density, temperature, and spacecraft frame charging. Results from IMESA currently orbiting on STPSat-3 are presented, showing frame charging effects dependent on a complex function of the number of solar panel cell strings switched in, solar panel current, and plasma density. IMESA will fly on four more satellites launching in the next two calendar years, enabling an undergraduate DoD space weather constellation in Low Earth Orbit that has the ability to significantly improve space weather forecasting capabilities using assimilative forecast models.

A long-range-corrected density functional that performs well for both ground-state properties and time-dependent density functional theory excitation energies, including charge-transfer excited states.

PubMed

Rohrdanz, Mary A; Martins, Katie M; Herbert, John M

2009-02-07

We introduce a hybrid density functional that asymptotically incorporates full Hartree-Fock exchange, based on the long-range-corrected exchange-hole model of Henderson et al. [J. Chem. Phys. 128, 194105 (2008)]. The performance of this functional, for ground-state properties and for vertical excitation energies within time-dependent density functional theory, is systematically evaluated, and optimal values are determined for the range-separation parameter, omega, and for the fraction of short-range Hartree-Fock exchange. We denote the new functional as LRC-omegaPBEh, since it reduces to the standard PBEh hybrid functional (also known as PBE0 or PBE1PBE) for a certain choice of its two parameters. Upon optimization of these parameters against a set of ground- and excited-state benchmarks, the LRC-omegaPBEh functional fulfills three important requirements: (i) It outperforms the PBEh hybrid functional for ground-state atomization energies and reaction barrier heights; (ii) it yields statistical errors comparable to PBEh for valence excitation energies in both small and medium-sized molecules; and (iii) its performance for charge-transfer excitations is comparable to its performance for valence excitations. LRC-omegaPBEh, with the parameters determined herein, is the first density functional that satisfies all three criteria. Notably, short-range Hartree-Fock exchange appears to be necessary in order to obtain accurate ground-state properties and vertical excitation energies using the same value of omega.

Ground-State Charge-Density Distribution in a Crystal of the Luminescent ortho-Phenylenediboronic Acid Complex with 8-Hydroxyquinoline.

PubMed

Jarzembska, Katarzyna N; Kamiński, Radosław; Durka, Krzysztof; Woźniak, Krzysztof

2018-05-10

This contribution is devoted to the first electron density studies of a luminescent oxyquinolinato boron complex in the solid state. ortho-Phenylenediboronic acid mixed with 8-hydroxyquinoline in dioxane forms high-quality single crystals via slow solvent evaporation, which allows successful high resolution data collection (sin θ/λ = 1.2 Å -1 ) and charge density distribution modeling. Particular attention has been paid to the boron-oxygen fragment connecting the two parts of the complex, and to the solvent species exhibiting anharmonic thermal motion. The experiment and theory compared rather well in terms of atomic charges and volumes, except for the boron centers. Boron atoms, as expected, constitute the most electron-deficient species in the complex molecule, whereas the neighboring oxygen and carbon atoms are the most significantly negatively charged ones. This part of the molecule appears to be very much involved in the charge transfer occurring between the acid fragment and oxyquinoline moiety leading to the observed fluorescence, as supported by the time-dependent density functional theory (TDDFT) results and the generated transition density maps. TDDFT calculations indicated that p-type atomic orbitals contributing to the HOMO-1, HOMO, and LUMO play the major role in the lowest energy transitions, and enabled further comparison with the charge density features, which is discussed in details. Furthermore, the results confirmed the known fact the Q ligand character is most important for the spectroscopic properties of this class of complexes.

Critical Role of the Exchange Interaction for the Electronic Structure and Charge-Density-Wave Formation in TiSe2

NASA Astrophysics Data System (ADS)

Hellgren, Maria; Baima, Jacopo; Bianco, Raffaello; Calandra, Matteo; Mauri, Francesco; Wirtz, Ludger

2017-10-01

We show that the inclusion of screened exchange via hybrid functionals provides a unified description of the electronic and vibrational properties of TiSe2 . In contrast to local approximations in density functional theory, the explicit inclusion of exact, nonlocal exchange captures the effects of the electron-electron interaction needed to both separate the Ti -d states from the Se -p states and stabilize the charge-density-wave (CDW) (or low-T ) phase through the formation of a p -d hybridized state. We further show that this leads to an enhanced electron-phonon coupling that can drive the transition even if a small gap opens in the high-T phase. Finally, we demonstrate that the hybrid functionals can generate a CDW phase where the electronic bands, the geometry, and the phonon frequencies are in agreement with experiments.

Understanding the conformational flexibility and electrostatic properties of curcumin in the active site of rhAChE via molecular docking, molecular dynamics, and charge density analysis.

PubMed

Saravanan, Kandasamy; Kalaiarasi, Chinnasamy; Kumaradhas, Poomani

2017-12-01

Acetylcholinesterase (AChE) is an important enzyme responsible for Alzheimer's disease, as per report, keto-enol form of curcumin inhibits this enzyme. The present study aims to understand the binding mechanism of keto-enol curcumin with the recombinant human Acetylcholinesterase (rhAChE) from its conformational flexibility, intermolecular interactions, charge density distribution, and the electrostatic properties at the active site of rhAChE. To accomplish this, a molecular docking analysis of curcumin with the rhAChE was performed, which gives the structure and conformation of curcumin in the active site of rhAChE. Further, the charge density distribution and the electrostatic properties of curcumin molecule (lifted from the active site of rhAChE) were determined from the high level density functional theory (DFT) calculations coupled with the charge density analysis. On the other hand, the curcumin molecule was optimized (gas phase) using DFT method and further, the structure and charge density analysis were also carried out. On comparing the conformation, charge density distribution and the electrostatic potential of the active site form of curcumin with the corresponding gas phase form reveals that the above said properties are significantly altered when curcumin is present in the active site of rhAChE. The conformational stability and the interaction of curcumin in the active site are also studied using molecular dynamics simulation, which shows a large variation in the conformational geometry of curcumin as well as the intermolecular interactions.

Electronic structures and magnetic/optical properties of metal phthalocyanine complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baba, Shintaro; Suzuki, Atsushi, E-mail: suzuki@mat.usp.ac.jp; Oku, Takeo

2016-02-01

Electronic structures and magnetic / optical properties of metal phthalocyanine complexes were studied by quantum calculations using density functional theory. Effects of central metal and expansion of π orbital on aromatic ring as conjugation system on the electronic structures, magnetic, optical properties and vibration modes of infrared and Raman spectra of metal phthalocyanines were investigated. Electron and charge density distribution and energy levels near frontier orbital and excited states were influenced by the deformed structures varied with central metal and charge. The magnetic parameters of chemical shifts in {sup 13}C-nuclear magnetic resonance ({sup 13}C-NMR), principle g-tensor, A-tensor, V-tensor of electricmore » field gradient and asymmetry parameters derived from the deformed structures with magnetic interaction of nuclear quadruple interaction based on electron and charge density distribution with a bias of charge near ligand under crystal field.« less

Density functional theory and chromium: Insights from the dimers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Würdemann, Rolf; Kristoffersen, Henrik H.; Moseler, Michael

2015-03-28

The binding in small Cr clusters is re-investigated, where the correct description of the dimer in three charge states is used as criterion to assign the most suitable density functional theory approximation. The difficulty in chromium arises from the subtle interplay between energy gain from hybridization and energetic cost due to exchange between s and d based molecular orbitals. Variations in published bond lengths and binding energies are shown to arise from insufficient numerical representation of electron density and Kohn-Sham wave-functions. The best functional performance is found for gradient corrected (GGA) functionals and meta-GGAs, where we find severe differences betweenmore » functionals from the same family due to the importance of exchange. Only the “best fit” from Bayesian error estimation is able to predict the correct energetics for all three charge states unambiguously. With this knowledge, we predict small bond-lengths to be exclusively present in Cr{sub 2} and Cr{sub 2}{sup −}. Already for the dimer cation, solely long bond-lengths appear, similar to what is found in the trimer and in chromium bulk.« less

Unique magnetic and thermoelectric properties of chemically functionalized narrow carbon polymers.

PubMed

Zberecki, K; Wierzbicki, M; Swirkowicz, R; Barnaś, J

2017-02-01

We analyze magnetic, transport and thermoelectric properties of narrow carbon polymers, which are chemically functionalized with nitroxide groups. Numerical calculations of the electronic band structure and the corresponding transmission function are based on density functional theory. Transport and thermoelectric parameters are calculated in the linear response regime, with particular interest in charge and spin thermopowers (charge and spin Seebeck effects). Such nanoribbons are shown to have thermoelectric properties described by large thermoelectric efficiency, which makes these materials promising from the application point of view.

Sensing local pH and ion concentration at graphene electrode surfaces using in situ Raman spectroscopy.

PubMed

Shi, Haotian; Poudel, Nirakar; Hou, Bingya; Shen, Lang; Chen, Jihan; Benderskii, Alexander V; Cronin, Stephen B

2018-02-01

We report a novel approach to probe the local ion concentration at graphene/water interfaces using in situ Raman spectroscopy. Here, the upshifts observed in the G band Raman mode under applied electrochemical potentials are used to determine the charge density in the graphene sheet. For voltages up to ±0.8 V vs. NHE, we observe substantial upshifts in the G band Raman mode by as much as 19 cm -1 , which corresponds to electron and hole carrier densities of 1.4 × 10 13 cm -2 and Fermi energy shifts of ±430 meV. The charge density in the graphene electrode is also measured independently using the capacitance-voltage characteristics (i.e., Q = CV), and is found to be consistent with those measured by Raman spectroscopy. From charge neutrality requirements, the ion concentration in solution per unit area must be equal and opposite to the charge density in the graphene electrode. Based on these charge densities, we estimate the local ion concentration as a function of electrochemical potential in both pure DI water and 1 M KCl solutions, which span a pH range from 3.8 to 10.4 for pure DI water and net ion concentrations of ±0.7 mol L -1 for KCl under these applied voltages.

Anisotropy-driven transition from the Moore-Read state to quantum Hall stripes

NASA Astrophysics Data System (ADS)

Zhu, Zheng; Sodemann, Inti; Sheng, D. N.; Fu, Liang

2017-05-01

We investigate the nature of the quantum Hall liquid in a half-filled second Landau level (n =1 ) as a function of band mass anisotropy using numerical exact diagonalization and density matrix renormalization group methods. We find increasing the mass anisotropy induces a quantum phase transition from the Moore-Read state to a charge density wave state. By analyzing the energy spectrum, guiding center structure factors, and by adding weak pinning potentials, we show that this charge density wave is a unidirectional quantum Hall stripe, which has a periodicity of a few magnetic lengths and survives in the thermodynamic limit. We find smooth profiles for the guiding center occupation function that reveal the strong coupling nature of the array of chiral Luttinger liquids residing at the stripe edges.

Charge-transfer potentials for ionic crystals: Cauchy violation, LO-TO splitting, and the necessity of an ionic reference state.

PubMed

Sukhomlinov, Sergey V; Müser, Martin H

2015-12-14

In this work, we study how including charge transfer into force fields affects the predicted elastic and vibrational Γ-point properties of ionic crystals, in particular those of rock salt. In both analytical and numerical calculations, we find that charge transfer generally leads to a negative contribution to the Cauchy pressure, P(C) ≡ C12 - C66, where C12 and C66 are elements of the elastic tensor. This contribution increases in magnitude with pressure for different charge-transfer approaches in agreement with results obtained with density functional theory (DFT). However, details of the charge-transfer models determine the pressure dependence of the longitudinal optical-transverse optical splitting and that for partial charges. These last two quantities increase with density as long as the chemical hardness depends at most weakly on the environment while experiments and DFT find a decrease. In order to reflect the correct trends, the charge-transfer expansion has to be made around ions and the chemical (bond) hardness has to increase roughly exponentially with inverse density or bond lengths. Finally, the adjustable force-field parameters only turn out meaningful, when the expansion is made around ions.

Charge-transfer potentials for ionic crystals: Cauchy violation, LO-TO splitting, and the necessity of an ionic reference state

NASA Astrophysics Data System (ADS)

Sukhomlinov, Sergey V.; Müser, Martin H.

2015-12-01

In this work, we study how including charge transfer into force fields affects the predicted elastic and vibrational Γ-point properties of ionic crystals, in particular those of rock salt. In both analytical and numerical calculations, we find that charge transfer generally leads to a negative contribution to the Cauchy pressure, PC ≡ C12 - C66, where C12 and C66 are elements of the elastic tensor. This contribution increases in magnitude with pressure for different charge-transfer approaches in agreement with results obtained with density functional theory (DFT). However, details of the charge-transfer models determine the pressure dependence of the longitudinal optical-transverse optical splitting and that for partial charges. These last two quantities increase with density as long as the chemical hardness depends at most weakly on the environment while experiments and DFT find a decrease. In order to reflect the correct trends, the charge-transfer expansion has to be made around ions and the chemical (bond) hardness has to increase roughly exponentially with inverse density or bond lengths. Finally, the adjustable force-field parameters only turn out meaningful, when the expansion is made around ions.

The charger transfer electronic coupling in diabatic perspective: A multi-state density functional theory study

NASA Astrophysics Data System (ADS)

Guo, Xinwei; Qu, Zexing; Gao, Jiali

2018-01-01

The multi-state density functional theory (MSDFT) provides a convenient way to estimate electronic coupling of charge transfer processes based on a diabatic representation. Its performance has been benchmarked against the HAB11 database with a mean unsigned error (MUE) of 17 meV between MSDFT and ab initio methods. The small difference may be attributed to different representations, diabatic from MSDFT and adiabatic from ab initio calculations. In this discussion, we conclude that MSDFT provides a general and efficient way to estimate the electronic coupling for charge-transfer rate calculations based on the Marcus-Hush model.

Vibrational Spectra and Density functional calculation of Organic Nonlinear Optic Crystal p-Amino Acetanilide

NASA Astrophysics Data System (ADS)

Saja, D.; Joe, I. Hubert; Jayakumar, V. S.

2006-01-01

The NIR-FT Raman, FT-IR spectral analysis of potential NLO material P-Amino Acetanilide is carried out by density functional computations. The optimized geometry shows that NH2 and NHCOCH3 groups substituted in para position of phenyl ring are non-planar which predicts maximum conjugation of molecule with donor and acceptor groups. Vibrational analysis reveals that simultaneous IR and Raman activation of the phenyl ring modes also provide evidence for the charge transfer interaction between the donors and the acceptor can make the molecule highly polarized and the intra molecular charge transfer interaction must be responsible for the NLO properties of PAA.

Charge relaxation and dynamics in organic semiconductors

NASA Astrophysics Data System (ADS)

Kwok, H. L.

2006-08-01

Charge relaxation in dispersive materials is often described in terms of the stretched exponential function (Kohlrausch law). The process can be explained using a "hopping" model which in principle, also applies to charge transport such as current conduction. This work analyzed reported transient photoconductivity data on functionalized pentacene single crystals using a geometric hopping model developed by B. Sturman et al and extracted values (or range of values) on the materials parameters relevant to charge relaxation as well as charge transport. Using the correlated disorder model (CDM), we estimated values of the carrier mobility for the pentacene samples. From these results, we observed the following: i) the transport site density appeared to be of the same order of magnitude as the carrier density; ii) it was possible to extract lower bound values on the materials parameters linked to the transport process; and iii) by matching the simulated charge decay to the transient photoconductivity data, we were able to refine estimates on the materials parameters. The data also allowed us to simulate the stretched exponential decay. Our observations suggested that the stretching index and the carrier mobility were related. Physically, such interdependence would allow one to demarcate between localized molecular interactions and distant coulomb interactions.

Screening of charged impurities as a possible mechanism for conductance change in graphene gas sensing

NASA Astrophysics Data System (ADS)

Liang, Sang-Zi; Chen, Gugang; Harutyunyan, Avetik R.; Sofo, Jorge O.

2014-09-01

In carbon nanotube and graphene gas sensing, the measured conductance change after the sensor is exposed to target molecules has been traditionally attributed to carrier density change due to charge transfer between the sample and the adsorbed molecule. However, this explanation has many problems when it is applied to graphene: The increased amount of Coulomb impurities should lead to decrease in carrier mobility which was not observed in many experiments, carrier density is controlled by the gate voltage in the experimental setup, and there are inconsistencies in the energetics of the charge transfer. In this paper we explore an alternative mechanism. Charged functional groups and dipolar molecules on the surface of graphene may counteract the effect of charged impurities on the substrate. Because scattering of electrons with these charged impurities has been shown to be the limiting factor in graphene conductivity, this leads to significant changes in the transport behavior. A model for the conductivity is established using the random phase approximation dielectric function of graphene and the first-order Born approximation for scattering. The model predicts optimal magnitudes for the charge and dipole moment which maximally screen a given charged impurity. The dipole screening is shown to be generally weaker than the charge screening although the former becomes more effective with higher gate voltage away from the charge neutrality point. The model also predicts that with increasing amount of adsorbates, the charge impurities eventually become saturated and additional adsorption always lead to decreasing conductivity.

Quantitative analysis of the guest-concentration dependence of the mobility in a disordered fluorene-arylamine host-guest system in the guest-to-guest regime

NASA Astrophysics Data System (ADS)

Nicolai, H. T.; Hof, A. J.; Lu, M.; Blom, P. W. M.; de Vries, R. J.; Coehoorn, R.

2011-11-01

The charge transport in a polyspirobifluorene derivative with copolymerized N,N,N',N'-tetraaryldiamino biphenyl (TAD) hole transport units is investigated as a function of the TAD content. For TAD concentrations larger than 5%, guest-to-guest transport is observed. It is demonstrated that in this regime the charge carrier density dependent mobility can be described consistently with the extended Gaussian disorder model, with a density of hopping sites which is proportional to the TAD concentration and comparable to the molecular density.

Accurate image-charge method by the use of the residue theorem for core-shell dielectric sphere

NASA Astrophysics Data System (ADS)

Fu, Jing; Xu, Zhenli

2018-02-01

An accurate image-charge method (ICM) is developed for ionic interactions outside a core-shell structured dielectric sphere. Core-shell particles have wide applications for which the theoretical investigation requires efficient methods for the Green's function used to calculate pairwise interactions of ions. The ICM is based on an inverse Mellin transform from the coefficients of spherical harmonic series of the Green's function such that the polarization charge due to dielectric boundaries is represented by a series of image point charges and an image line charge. The residue theorem is used to accurately calculate the density of the line charge. Numerical results show that the ICM is promising in fast evaluation of the Green's function, and thus it is useful for theoretical investigations of core-shell particles. This routine can also be applicable for solving other problems with spherical dielectric interfaces such as multilayered media and Debye-Hückel equations.

Charge characteristics of humic and fulvic acids: comparative analysis by colloid titration and potentiometric titration with continuous pK-distribution function model.

PubMed

Bratskaya, S; Golikov, A; Lutsenko, T; Nesterova, O; Dudarchik, V

2008-09-01

Charge characteristics of humic and fulvic acids of a different origin (inshore soils, peat, marine sediments, and soil (lysimetric) waters) were evaluated by means of two alternative methods - colloid titration and potentiometric titration. In order to elucidate possible limitations of the colloid titration as an express method of analysis of low content of humic substances we monitored changes in acid-base properties and charge densities of humic substances with soil depth, fractionation, and origin. We have shown that both factors - strength of acidic groups and molecular weight distribution in humic and fulvic acids - can affect the reliability of colloid titration. Due to deviations from 1:1 stoichiometry in interactions of humic substances with polymeric cationic titrant, the colloid titration can underestimate total acidity (charge density) of humic substances with domination of weak acidic functional groups (pK>6) and high content of the fractions with molecular weight below 1kDa.

J/ψ production as a function of charged-particle pseudorapidity density in p-Pb collisions at √{sNN } = 5.02TeV

NASA Astrophysics Data System (ADS)

Adamová, D.; Aggarwal, M. M.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, N.; Ahn, S. U.; Aiola, S.; Akindinov, A.; Alam, S. N.; Albuquerque, D. S. D.; Aleksandrov, D.; Alessandro, B.; Alexandre, D.; Alfaro Molina, R.; Alici, A.; Alkin, A.; Alme, J.; Alt, T.; Altsybeev, I.; Alves Garcia Prado, C.; An, M.; Andrei, C.; Andrews, H. A.; Andronic, A.; Anguelov, V.; Anson, C.; Antičić, T.; Antinori, F.; Antonioli, P.; Anwar, R.; Aphecetche, L.; Appelshäuser, H.; Arcelli, S.; Arnaldi, R.; Arnold, O. W.; Arsene, I. C.; Arslandok, M.; Audurier, B.; Augustinus, A.; Averbeck, R.; Azmi, M. D.; Badalà, A.; Baek, Y. W.; Bagnasco, S.; Bailhache, R.; Bala, R.; Baldisseri, A.; Ball, M.; Baral, R. C.; Barbano, A. M.; Barbera, R.; Barile, F.; Barioglio, L.; Barnaföldi, G. G.; Barnby, L. S.; Barret, V.; Bartalini, P.; Barth, K.; Bartke, J.; Bartsch, E.; Basile, M.; Bastid, N.; Basu, S.; Bathen, B.; Batigne, G.; Batista Camejo, A.; Batyunya, B.; Batzing, P. C.; Bearden, I. G.; Beck, H.; Bedda, C.; Behera, N. K.; Belikov, I.; Bellini, F.; Bello Martinez, H.; Bellwied, R.; Beltran, L. G. E.; Belyaev, V.; Bencedi, G.; Beole, S.; Bercuci, A.; Berdnikov, Y.; Berenyi, D.; Bertens, R. A.; Berzano, D.; Betev, L.; Bhasin, A.; Bhat, I. R.; Bhati, A. K.; Bhattacharjee, B.; Bhom, J.; Bianchi, L.; Bianchi, N.; Bianchin, C.; Bielčík, J.; Bielčíková, J.; Bilandzic, A.; Biro, G.; Biswas, R.; Biswas, S.; Blair, J. T.; Blau, D.; Blume, C.; Boca, G.; Bock, F.; Bogdanov, A.; Boldizsár, L.; Bombara, M.; Bonomi, G.; Bonora, M.; Book, J.; Borel, H.; Borissov, A.; Borri, M.; Botta, E.; Bourjau, C.; Braun-Munzinger, P.; Bregant, M.; Broker, T. A.; Browning, T. A.; Broz, M.; Brucken, E. J.; Bruna, E.; Bruno, G. E.; Budnikov, D.; Buesching, H.; Bufalino, S.; Buhler, P.; Buitron, S. A. I.; Buncic, P.; Busch, O.; Buthelezi, Z.; Butt, J. B.; Buxton, J. T.; Cabala, J.; Caffarri, D.; Caines, H.; Caliva, A.; Calvo Villar, E.; Camerini, P.; Capon, A. A.; Carena, F.; Carena, W.; Carnesecchi, F.; Castillo Castellanos, J.; Castro, A. J.; Casula, E. A. R.; Ceballos Sanchez, C.; Cerello, P.; Chang, B.; Chapeland, S.; Chartier, M.; Charvet, J. L.; Chattopadhyay, S.; Chattopadhyay, S.; Chauvin, A.; Cherney, M.; Cheshkov, C.; Cheynis, B.; Chibante Barroso, V.; Chinellato, D. D.; Cho, S.; Chochula, P.; Choi, K.; Chojnacki, M.; Choudhury, S.; Christakoglou, P.; Christensen, C. H.; Christiansen, P.; Chujo, T.; Chung, S. U.; Cicalo, C.; Cifarelli, L.; Cindolo, F.; Cleymans, J.; Colamaria, F.; Colella, D.; Collu, A.; Colocci, M.; Conesa Balbastre, G.; Conesa Del Valle, Z.; Connors, M. E.; Contreras, J. G.; Cormier, T. M.; Corrales Morales, Y.; Cortés Maldonado, I.; Cortese, P.; Cosentino, M. R.; Costa, F.; Costanza, S.; Crkovská, J.; Crochet, P.; Cuautle, E.; Cunqueiro, L.; Dahms, T.; Dainese, A.; Danisch, M. C.; Danu, A.; Das, D.; Das, I.; Das, S.; Dash, A.; Dash, S.; de, S.; de Caro, A.; de Cataldo, G.; de Conti, C.; de Cuveland, J.; de Falco, A.; de Gruttola, D.; De Marco, N.; de Pasquale, S.; de Souza, R. D.; Degenhardt, H. F.; Deisting, A.; Deloff, A.; Deplano, C.; Dhankher, P.; di Bari, D.; di Mauro, A.; di Nezza, P.; di Ruzza, B.; Diaz Corchero, M. A.; Dietel, T.; Dillenseger, P.; Divià, R.; Djuvsland, Ø.; Dobrin, A.; Domenicis Gimenez, D.; Dönigus, B.; Dordic, O.; Drozhzhova, T.; Dubey, A. K.; Dubla, A.; Ducroux, L.; Duggal, A. K.; Dupieux, P.; Ehlers, R. J.; Elia, D.; Endress, E.; Engel, H.; Epple, E.; Erazmus, B.; Erhardt, F.; Espagnon, B.; Esumi, S.; Eulisse, G.; Eum, J.; Evans, D.; Evdokimov, S.; Fabbietti, L.; Faivre, J.; Fantoni, A.; Fasel, M.; Feldkamp, L.; Feliciello, A.; Feofilov, G.; Ferencei, J.; Fernández Téllez, A.; Ferreiro, E. G.; Ferretti, A.; Festanti, A.; Feuillard, V. J. G.; Figiel, J.; Figueredo, M. A. S.; Filchagin, S.; Finogeev, D.; Fionda, F. M.; Fiore, E. M.; Floris, M.; Foertsch, S.; Foka, P.; Fokin, S.; Fragiacomo, E.; Francescon, A.; Francisco, A.; Frankenfeld, U.; Fronze, G. G.; Fuchs, U.; Furget, C.; Furs, A.; Fusco Girard, M.; Gaardhøje, J. J.; Gagliardi, M.; Gago, A. M.; Gajdosova, K.; Gallio, M.; Galvan, C. D.; Ganoti, P.; Gao, C.; Garabatos, C.; Garcia-Solis, E.; Garg, K.; Garg, P.; Gargiulo, C.; Gasik, P.; Gauger, E. F.; Gay Ducati, M. B.; Germain, M.; Ghosh, P.; Ghosh, S. K.; Gianotti, P.; Giubellino, P.; Giubilato, P.; Gladysz-Dziadus, E.; Glässel, P.; Goméz Coral, D. M.; Gomez Ramirez, A.; Gonzalez, A. S.; Gonzalez, V.; González-Zamora, P.; Gorbunov, S.; Görlich, L.; Gotovac, S.; Grabski, V.; Graczykowski, L. K.; Graham, K. L.; Greiner, L.; Grelli, A.; Grigoras, C.; Grigoriev, V.; Grigoryan, A.; Grigoryan, S.; Grion, N.; Gronefeld, J. M.; Grosa, F.; Grosse-Oetringhaus, J. F.; Grosso, R.; Gruber, L.; Grull, F. R.; Guber, F.; Guernane, R.; Guerzoni, B.; Gulbrandsen, K.; Gunji, T.; Gupta, A.; Gupta, R.; Guzman, I. B.; Haake, R.; Hadjidakis, C.; Hamagaki, H.; Hamar, G.; Hamon, J. C.; Harris, J. W.; Harton, A.; Hatzifotiadou, D.; Hayashi, S.; Heckel, S. T.; Hellbär, E.; Helstrup, H.; Herghelegiu, A.; Herrera Corral, G.; Herrmann, F.; Hess, B. A.; Hetland, K. F.; Hillemanns, H.; Hippolyte, B.; Hladky, J.; Hohlweger, B.; Horak, D.; Hosokawa, R.; Hristov, P.; Hughes, C.; Humanic, T. J.; Hussain, N.; Hussain, T.; Hutter, D.; Hwang, D. S.; Ilkaev, R.; Inaba, M.; Ippolitov, M.; Irfan, M.; Isakov, V.; Islam, M. S.; Ivanov, M.; Ivanov, V.; Izucheev, V.; Jacak, B.; Jacazio, N.; Jacobs, P. M.; Jadhav, M. B.; Jadlovska, S.; Jadlovsky, J.; Jaelani, S.; Jahnke, C.; Jakubowska, M. J.; Janik, M. A.; Jayarathna, P. H. S. Y.; Jena, C.; Jena, S.; Jercic, M.; Jimenez Bustamante, R. T.; Jones, P. G.; Jusko, A.; Kalinak, P.; Kalweit, A.; Kang, J. H.; Kaplin, V.; Kar, S.; Karasu Uysal, A.; Karavichev, O.; Karavicheva, T.; Karayan, L.; Karpechev, E.; Kebschull, U.; Keidel, R.; Keijdener, D. L. D.; Keil, M.; Ketzer, B.; Mohisin Khan, M.; Khan, P.; Khan, S. A.; Khanzadeev, A.; Kharlov, Y.; Khatun, A.; Khuntia, A.; Kielbowicz, M. M.; Kileng, B.; Kim, D. W.; Kim, D. J.; Kim, D.; Kim, H.; Kim, J. S.; Kim, J.; Kim, M.; Kim, M.; Kim, S.; Kim, T.; Kirsch, S.; Kisel, I.; Kiselev, S.; Kisiel, A.; Kiss, G.; Klay, J. L.; Klein, C.; Klein, J.; Klein-Bösing, C.; Klewin, S.; Kluge, A.; Knichel, M. L.; Knospe, A. G.; Kobdaj, C.; Kofarago, M.; Kollegger, T.; Kolojvari, A.; Kondratiev, V.; Kondratyeva, N.; Kondratyuk, E.; Konevskikh, A.; Kopcik, M.; Kour, M.; Kouzinopoulos, C.; Kovalenko, O.; Kovalenko, V.; Kowalski, M.; Koyithatta Meethaleveedu, G.; Králik, I.; Kravčáková, A.; Krivda, M.; Krizek, F.; Kryshen, E.; Krzewicki, M.; Kubera, A. M.; Kučera, V.; Kuhn, C.; Kuijer, P. G.; Kumar, A.; Kumar, J.; Kumar, L.; Kumar, S.; Kundu, S.; Kurashvili, P.; Kurepin, A.; Kurepin, A. B.; Kuryakin, A.; Kushpil, S.; Kweon, M. J.; Kwon, Y.; La Pointe, S. L.; La Rocca, P.; Lagana Fernandes, C.; Lakomov, I.; Langoy, R.; Lapidus, K.; Lara, C.; Lardeux, A.; Lattuca, A.; Laudi, E.; Lavicka, R.; Lazaridis, L.; Lea, R.; Leardini, L.; Lee, S.; Lehas, F.; Lehner, S.; Lehrbach, J.; Lemmon, R. C.; Lenti, V.; Leogrande, E.; León Monzón, I.; Lévai, P.; Li, S.; Li, X.; Lien, J.; Lietava, R.; Lindal, S.; Lindenstruth, V.; Lippmann, C.; Lisa, M. A.; Litichevskyi, V.; Ljunggren, H. M.; Llope, W. J.; Lodato, D. F.; Loenne, P. I.; Loginov, V.; Loizides, C.; Loncar, P.; Lopez, X.; López Torres, E.; Lowe, A.; Luettig, P.; Lunardon, M.; Luparello, G.; Lupi, M.; Lutz, T. H.; Maevskaya, A.; Mager, M.; Mahajan, S.; Mahmood, S. M.; Maire, A.; Majka, R. D.; Malaev, M.; Maldonado Cervantes, I.; Malinina, L.; Mal'Kevich, D.; Malzacher, P.; Mamonov, A.; Manko, V.; Manso, F.; Manzari, V.; Mao, Y.; Marchisone, M.; Mareš, J.; Margagliotti, G. V.; Margotti, A.; Margutti, J.; Marín, A.; Markert, C.; Marquard, M.; Martin, N. A.; Martin Blanco, J.; Martinengo, P.; Martinez, J. A. L.; Martínez, M. I.; Martínez García, G.; Martinez Pedreira, M.; Mas, A.; Masciocchi, S.; Masera, M.; Masoni, A.; Mastroserio, A.; Mathis, A. M.; Matyja, A.; Mayer, C.; Mazer, J.; Mazzilli, M.; Mazzoni, M. A.; Meddi, F.; Melikyan, Y.; Menchaca-Rocha, A.; Meninno, E.; Mercado Pérez, J.; Meres, M.; Mhlanga, S.; Miake, Y.; Mieskolainen, M. M.; Mihaylov, D. L.; Mikhaylov, K.; Milano, L.; Milosevic, J.; Mischke, A.; Mishra, A. N.; Miśkowiec, D.; Mitra, J.; Mitu, C. M.; Mohammadi, N.; Mohanty, B.; Montes, E.; Moreira de Godoy, D. A.; Moreno, L. A. P.; Moretto, S.; Morreale, A.; Morsch, A.; Muccifora, V.; Mudnic, E.; Mühlheim, D.; Muhuri, S.; Mukherjee, M.; Mulligan, J. D.; Munhoz, M. G.; Münning, K.; Munzer, R. H.; Murakami, H.; Murray, S.; Musa, L.; Musinsky, J.; Myers, C. J.; Naik, B.; Nair, R.; Nandi, B. K.; Nania, R.; Nappi, E.; Naru, M. U.; Natal da Luz, H.; Nattrass, C.; Navarro, S. R.; Nayak, K.; Nayak, R.; Nayak, T. K.; Nazarenko, S.; Nedosekin, A.; Negrao de Oliveira, R. A.; Nellen, L.; Nesbo, S. V.; Ng, F.; Nicassio, M.; Niculescu, M.; Niedziela, J.; Nielsen, B. S.; Nikolaev, S.; Nikulin, S.; Nikulin, V.; Noferini, F.; Nomokonov, P.; Nooren, G.; Noris, J. C. C.; Norman, J.; Nyanin, A.; Nystrand, J.; Oeschler, H.; Oh, S.; Ohlson, A.; Okubo, T.; Olah, L.; Oleniacz, J.; Oliveira da Silva, A. C.; Oliver, M. H.; Onderwaater, J.; Oppedisano, C.; Orava, R.; Oravec, M.; Ortiz Velasquez, A.; Oskarsson, A.; Otwinowski, J.; Oyama, K.; Pachmayer, Y.; Pacik, V.; Pagano, D.; Pagano, P.; Paić, G.; Palni, P.; Pan, J.; Pandey, A. K.; Panebianco, S.; Papikyan, V.; Pappalardo, G. S.; Pareek, P.; Park, J.; Park, W. J.; Parmar, S.; Passfeld, A.; Pathak, S. P.; Paticchio, V.; Patra, R. N.; Paul, B.; Pei, H.; Peitzmann, T.; Peng, X.; Pereira, L. G.; Pereira da Costa, H.; Peresunko, D.; Perez Lezama, E.; Peskov, V.; Pestov, Y.; Petráček, V.; Petrov, V.; Petrovici, M.; Petta, C.; Pezzi, R. P.; Piano, S.; Pikna, M.; Pillot, P.; Pimentel, L. O. D. L.; Pinazza, O.; Pinsky, L.; Piyarathna, D. B.; Płoskoń, M.; Planinic, M.; Pluta, J.; Pochybova, S.; Podesta-Lerma, P. L. M.; Poghosyan, M. G.; Polichtchouk, B.; Poljak, N.; Poonsawat, W.; Pop, A.; Poppenborg, H.; Porteboeuf-Houssais, S.; Porter, J.; Pospisil, J.; Pozdniakov, V.; Prasad, S. K.; Preghenella, R.; Prino, F.; Pruneau, C. A.; Pshenichnov, I.; Puccio, M.; Puddu, G.; Pujahari, P.; Punin, V.; Putschke, J.; Qvigstad, H.; Rachevski, A.; Raha, S.; Rajput, S.; Rak, J.; Rakotozafindrabe, A.; Ramello, L.; Rami, F.; Rana, D. B.; Raniwala, R.; Raniwala, S.; Räsänen, S. S.; Rascanu, B. T.; Rathee, D.; Ratza, V.; Ravasenga, I.; Read, K. F.; Redlich, K.; Rehman, A.; Reichelt, P.; Reidt, F.; Ren, X.; Renfordt, R.; Reolon, A. R.; Reshetin, A.; Reygers, K.; Riabov, V.; Ricci, R. A.; Richert, T.; Richter, M.; Riedler, P.; Riegler, W.; Riggi, F.; Ristea, C.; Rodríguez Cahuantzi, M.; Røed, K.; Rogochaya, E.; Rohr, D.; Röhrich, D.; Rokita, P. S.; Ronchetti, F.; Ronflette, L.; Rosnet, P.; Rossi, A.; Rotondi, A.; Roukoutakis, F.; Roy, A.; Roy, C.; Roy, P.; Rubio Montero, A. J.; Rui, R.; Russo, R.; Rustamov, A.; Ryabinkin, E.; Ryabov, Y.; Rybicki, A.; Saarinen, S.; Sadhu, S.; Sadovsky, S.; Šafařík, K.; Saha, S. K.; Sahlmuller, B.; Sahoo, B.; Sahoo, P.; Sahoo, R.; Sahoo, S.; Sahu, P. K.; Saini, J.; Sakai, S.; Saleh, M. A.; Salzwedel, J.; Sambyal, S.; Samsonov, V.; Sandoval, A.; Sarkar, D.; Sarkar, N.; Sarma, P.; Sas, M. H. P.; Scapparone, E.; Scarlassara, F.; Scharenberg, R. P.; Scheid, H. S.; Schiaua, C.; Schicker, R.; Schmidt, C.; Schmidt, H. R.; Schmidt, M. O.; Schmidt, M.; Schuchmann, S.; Schukraft, J.; Schutz, Y.; Schwarz, K.; Schweda, K.; Scioli, G.; Scomparin, E.; Scott, R.; Šefčík, M.; Seger, J. E.; Sekiguchi, Y.; Sekihata, D.; Selyuzhenkov, I.; Senosi, K.; Senyukov, S.; Serradilla, E.; Sett, P.; Sevcenco, A.; Shabanov, A.; Shabetai, A.; Shadura, O.; Shahoyan, R.; Shangaraev, A.; Sharma, A.; Sharma, A.; Sharma, M.; Sharma, M.; Sharma, N.; Sheikh, A. I.; Shigaki, K.; Shou, Q.; Shtejer, K.; Sibiriak, Y.; Siddhanta, S.; Sielewicz, K. M.; Siemiarczuk, T.; Silvermyr, D.; Silvestre, C.; Simatovic, G.; Simonetti, G.; Singaraju, R.; Singh, R.; Singhal, V.; Sinha, T.; Sitar, B.; Sitta, M.; Skaali, T. B.; Slupecki, M.; Smirnov, N.; Snellings, R. J. M.; Snellman, T. W.; Song, J.; Song, M.; Soramel, F.; Sorensen, S.; Sozzi, F.; Spiriti, E.; Sputowska, I.; Srivastava, B. K.; Stachel, J.; Stan, I.; Stankus, P.; Stenlund, E.; Stiller, J. H.; Stocco, D.; Strmen, P.; Suaide, A. A. P.; Sugitate, T.; Suire, C.; Suleymanov, M.; Suljic, M.; Sultanov, R.; Šumbera, M.; Sumowidagdo, S.; Suzuki, K.; Swain, S.; Szabo, A.; Szarka, I.; Szczepankiewicz, A.; Szymanski, M.; Tabassam, U.; Takahashi, J.; Tambave, G. J.; Tanaka, N.; Tarhini, M.; Tariq, M.; Tarzila, M. G.; Tauro, A.; Tejeda Muñoz, G.; Telesca, A.; Terasaki, K.; Terrevoli, C.; Teyssier, B.; Thakur, D.; Thakur, S.; Thomas, D.; Tieulent, R.; Tikhonov, A.; Timmins, A. R.; Toia, A.; Tripathy, S.; Trogolo, S.; Trombetta, G.; Trubnikov, V.; Trzaska, W. H.; Trzeciak, B. A.; Tsuji, T.; Tumkin, A.; Turrisi, R.; Tveter, T. S.; Ullaland, K.; Umaka, E. N.; Uras, A.; Usai, G. L.; Utrobicic, A.; Vala, M.; van der Maarel, J.; van Hoorne, J. W.; van Leeuwen, M.; Vanat, T.; Vande Vyvre, P.; Varga, D.; Vargas, A.; Vargyas, M.; Varma, R.; Vasileiou, M.; Vasiliev, A.; Vauthier, A.; Vázquez Doce, O.; Vechernin, V.; Veen, A. M.; Velure, A.; Vercellin, E.; Vergara Limón, S.; Vernet, R.; Vértesi, R.; Vickovic, L.; Vigolo, S.; Viinikainen, J.; Vilakazi, Z.; Villalobos Baillie, O.; Villatoro Tello, A.; Vinogradov, A.; Vinogradov, L.; Virgili, T.; Vislavicius, V.; Vodopyanov, A.; Völkl, M. A.; Voloshin, K.; Voloshin, S. A.; Volpe, G.; von Haller, B.; Vorobyev, I.; Voscek, D.; Vranic, D.; Vrláková, J.; Wagner, B.; Wagner, J.; Wang, H.; Wang, M.; Watanabe, D.; Watanabe, Y.; Weber, M.; Weber, S. G.; Weiser, D. F.; Wessels, J. P.; Westerhoff, U.; Whitehead, A. M.; Wiechula, J.; Wikne, J.; Wilk, G.; Wilkinson, J.; Willems, G. A.; Williams, M. C. S.; Windelband, B.; Winn, M.; Witt, W. E.; Yalcin, S.; Yang, P.; Yano, S.; Yin, Z.; Yokoyama, H.; Yoo, I.-K.; Yoon, J. H.; Yurchenko, V.; Zaccolo, V.; Zaman, A.; Zampolli, C.; Zanoli, H. J. C.; Zardoshti, N.; Zarochentsev, A.; Závada, P.; Zaviyalov, N.; Zbroszczyk, H.; Zhalov, M.; Zhang, H.; Zhang, X.; Zhang, Y.; Zhang, C.; Zhang, Z.; Zhao, C.; Zhigareva, N.; Zhou, D.; Zhou, Y.; Zhou, Z.; Zhu, H.; Zhu, J.; Zhu, X.; Zichichi, A.; Zimmermann, A.; Zimmermann, M. B.; Zimmermann, S.; Zinovjev, G.; Zmeskal, J.; Alice Collaboration<

2018-01-01

We report measurements of the inclusive J/ψ yield and average transverse momentum as a function of charged-particle pseudorapidity density dNch / dη in p-Pb collisions at √{sNN } = 5.02TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/ψ yield with normalised dNch / dη, measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/ψ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity.

J/ψ production as a function of charged-particle pseudorapidity density in p–Pb collisions at s NN = 5.02 TeV

DOE PAGES

Adamová, D.; Aggarwal, M. M.; Aglieri Rinella, G.; ...

2017-11-08

Here, we report measurements of the inclusive J/ψ yield and average transverse momentum as a function of charged-particle pseudorapidity density dN ch/dη in p–Pb collisions atmore » $$\\sqrt{s}$$$_ {NN}$$ = 5.02 TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/ψ yield with normalised dN ch/dη, measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/ψ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity.« less

J/ψ production as a function of charged-particle pseudorapidity density in p–Pb collisions at s NN = 5.02 TeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adamová, D.; Aggarwal, M. M.; Aglieri Rinella, G.

Here, we report measurements of the inclusive J/ψ yield and average transverse momentum as a function of charged-particle pseudorapidity density dN ch/dη in p–Pb collisions atmore » $$\\sqrt{s}$$$_ {NN}$$ = 5.02 TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/ψ yield with normalised dN ch/dη, measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/ψ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity.« less

Comparison of Molecular Dynamics with Classical Density Functional and Poisson–Boltzmann Theories of the Electric Double Layer in Nanochannels

PubMed Central

2012-01-01

Comparisons are made among Molecular Dynamics (MD), Classical Density Functional Theory (c-DFT), and Poisson–Boltzmann (PB) modeling of the electric double layer (EDL) for the nonprimitive three component model (3CM) in which the two ion species and solvent molecules are all of finite size. Unlike previous comparisons between c-DFT and Monte Carlo (MC), the present 3CM incorporates Lennard-Jones interactions rather than hard-sphere and hard-wall repulsions. c-DFT and MD results are compared over normalized surface charges ranging from 0.2 to 1.75 and bulk ion concentrations from 10 mM to 1 M. Agreement between the two, assessed by electric surface potential and ion density profiles, is found to be quite good. Wall potentials predicted by PB begin to depart significantly from c-DFT and MD for charge densities exceeding 0.3. Successive layers are observed to charge in a sequential manner such that the solvent becomes fully excluded from each layer before the onset of the next layer. Ultimately, this layer filling phenomenon results in fluid structures, Debye lengths, and electric surface potentials vastly different from the classical PB predictions. PMID:23316120

Effects of Acids, Bases, and Heteroatoms on Proximal Radial Distribution Functions for Proteins

PubMed Central

Nguyen, Bao Linh; Pettitt, B. Montgomery

2015-01-01

The proximal distribution of water around proteins is a convenient method of quantifying solvation. We consider the effect of charged and sulfur-containing amino acid side-chain atoms on the proximal radial distribution function (pRDF) of water molecules around proteins using side-chain analogs. The pRDF represents the relative probability of finding any solvent molecule at a distance from the closest or surface perpendicular protein atom. We consider the near-neighbor distribution. Previously, pRDFs were shown to be universal descriptors of the water molecules around C, N, and O atom types across hundreds of globular proteins. Using averaged pRDFs, a solvent density around any globular protein can be reconstructed with controllable relative error. Solvent reconstruction using the additional information from charged amino acid side-chain atom types from both small models and protein averages reveals the effects of surface charge distribution on solvent density and improves the reconstruction errors relative to simulation. Solvent density reconstructions from the small-molecule models are as effective and less computationally demanding than reconstructions from full macromolecular models in reproducing preferred hydration sites and solvent density fluctuations. PMID:26388706

Simulation of Charged Systems in Heterogeneous Dielectric Media via a True Energy Functional

NASA Astrophysics Data System (ADS)

Jadhao, Vikram; Solis, Francisco J.; de la Cruz, Monica Olvera

2012-11-01

For charged systems in heterogeneous dielectric media, a key obstacle for molecular dynamics (MD) simulations is the need to solve the Poisson equation in the media. This obstacle can be bypassed using MD methods that treat the local polarization charge density as a dynamic variable, but such approaches require access to a true free energy functional, one that evaluates to the equilibrium electrostatic energy at its minimum. In this Letter, we derive the needed functional. As an application, we develop a Car-Parrinello MD method for the simulation of free charges present near a spherical emulsion droplet separating two immiscible liquids with different dielectric constants. Our results show the presence of nonmonotonic ionic profiles in the dielectric with a lower dielectric constant.

Charge Separation and Exciton Dynamics at Polymer/ZnO Interface from First-Principles Simulations.

PubMed

Wu, Guangfen; Li, Zi; Zhang, Xu; Lu, Gang

2014-08-07

Charge separation and exciton dynamics play a crucial role in determining the performance of excitonic photovoltaics. Using time-dependent density functional theory with a range-separated exchange-correlation functional as well as nonadiabatic ab initio molecular dynamics, we have studied the formation and dynamics of charge-transfer (CT) excitons at polymer/ZnO interface. The interfacial atomic structure, exciton density of states and conversions between exciton species are examined from first-principles. The exciton dynamics exhibits both adiabatic and nonadiabatic characters. While the adiabatic transitions are facilitated by C═C vibrations along the polymer (P3HT) backbone, the nonadiabatic transitions are realized by exciton hopping between the excited states. We find that the localized ZnO surface states lead to localized low-energy CT states and poor charge separation. In contrast, the surface states of crystalline C60 are indistinguishable from the bulk states, resulting in delocalized CT states and efficient charge separation in polymer/fullerene (P3HT/PCBM) heterojunctions. The hot CT states are found to cool down in an ultrafast time scale and may not play a major role in charge separation of P3HT/ZnO. Finally we suggest that the dimensions of nanostructured acceptors can be tuned to obtain both efficient charge separation and high open circuit voltages.

Charged nanoparticle attraction in multivalent salt solution: A classical-fluids density functional theory and molecular dynamics study

DOE PAGES

Salerno, K. Michael; Frischknecht, Amalie L.; Stevens, Mark J.

2016-04-08

Here, negatively charged nanoparticles (NPs) in 1:1, 1:2, and 1:3 electrolyte solutions are studied in a primitive ion model using molecular dynamics (MD) simulations and classical density functional theory (DFT). We determine the conditions for attractive interactions between the like-charged NPs. Ion density profiles and NP–NP interaction free energies are compared between the two methods and are found to be in qualitative agreement. The NP interaction free energy is purely repulsive for monovalent counterions, but can be attractive for divalent and trivalent counterions. Using DFT, the NP interaction free energy for different NP diameters and charges is calculated. The depthmore » and location of the minimum in the interaction depend strongly on the NPs’ charge. For certain parameters, the depth of the attractive well can reach 8–10 k BT, indicating that kinetic arrest and aggregation of the NPs due to electrostatic interactions is possible. Rich behavior arises from the geometric constraints of counterion packing at the NP surface. Layering of counterions around the NPs is observed and, as secondary counterion layers form the minimum of the NP–NP interaction free energy shifts to larger separation, and the depth of the free energy minimum varies dramatically. We find that attractive interactions occur with and without NP overcharging.« less

Rare earth substitutional impurities in germanium: A hybrid density functional theory study

NASA Astrophysics Data System (ADS)

Igumbor, E.; Omotoso, E.; Tunhuma, S. M.; Danga, H. T.; Meyer, W. E.

2017-10-01

The Heyd, Scuseria, and Ernzerhof (HSE06) hybrid functional by means of density functional theory has been used to model the electronic and structural properties of rare earth (RE) substitutional impurities in germanium (REGe) . The formation and charge state transition energies for the REGe (RE = Ce, Pr, Er and Eu) were calculated. The energy of formation for the neutral charge state of the REGe lies between -0.14 and 3.13 eV. The formation energy result shows that the Pr dopant in Ge (PrGe) has the lowest formation energy of -0.14 eV, and is most energetically favourable under equilibrium conditions. The REGe induced charge state transition levels within the band gap of Ge. Shallow acceptor levels were induced by both the Eu (EuGe) and Pr (PrGe) dopants in Ge. The CeGe and ErGe exhibited properties of negative-U ordering with effective-U values of -0.85 and -1.07 eV, respectively.

Binding and Diffusion of Lithium in Graphite: Quantum Monte Carlo Benchmarks and Validation of van der Waals Density Functional Methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ganesh, P.; Kim, Jeongnim; Park, Changwon

2014-11-03

In highly accurate diffusion quantum Monte Carlo (QMC) studies of the adsorption and diffusion of atomic lithium in AA-stacked graphite are compared with van der Waals-including density functional theory (DFT) calculations. Predicted QMC lattice constants for pure AA graphite agree with experiment. Pure AA-stacked graphite is shown to challenge many van der Waals methods even when they are accurate for conventional AB graphite. Moreover, the highest overall DFT accuracy, considering pure AA-stacked graphite as well as lithium binding and diffusion, is obtained by the self-consistent van der Waals functional vdW-DF2, although errors in binding energies remain. Empirical approaches based onmore » point charges such as DFT-D are inaccurate unless the local charge transfer is assessed. Our results demonstrate that the lithium carbon system requires a simultaneous highly accurate description of both charge transfer and van der Waals interactions, favoring self-consistent approaches.« less

Adsorption and oxidation of SO2 by graphene oxides: A van der Waals density functional theory study

NASA Astrophysics Data System (ADS)

Zhang, Huijuan; Cen, Wanglai; Liu, Jie; Guo, Jiaxiu; Yin, Huaqiang; Ning, Ping

2015-01-01

Carbon materials have been used for low temperature (20-150 °C) catalytic removal of SO2 from the coal-burned flue gases for a long time, but the mechanism at atomic level is still controversial. Density functional theory was used to investigate the adsorption and oxidation of SO2 on elaborated graphene oxides (GOs) to discover the insights. It is found that the hydroxyl groups on GO surface possess bi-functional effects: both enhancing the adsorption of SO2 through H-bonding interaction and reducing the reaction barrier for its oxidation to SO3. The promotion of oxidation is related to a pre-activation of the surface epoxy group. Based on Bader population, charge difference and electron localization function analysis, a charge transfer channel is proposed to explain the pre-activation.

Peripheral transverse densities of the baryon octet from chiral effective field theory and dispersion analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alarcón, J. M.; Hiller Blin, A. N.; Vicente Vacas, M. J.

2017-05-08

The baryon electromagnetic form factors are expressed in terms of two-dimensional densities describing the distribution of charge and magnetization in transverse space at fixed light-front time. In this paper, we calculate the transverse densities of the spin-1/2 flavor-octet baryons at peripheral distances b=O(Mmore » $$-1\\atop{π}$$) using methods of relativistic chiral effective field theory (χ EFT) and dispersion analysis. The densities are represented as dispersive integrals over the imaginary parts of the form factors in the timelike region (spectral functions). The isovector spectral functions on the two-pion cut t > 4 M$$2\\atop{π}$$ are calculated using relativistic χEFT including octet and decuplet baryons. The χEFT calculations are extended into the ρ meson mass region using an N/D method that incorporates the pion electromagnetic form factor data. The isoscalar spectral functions are modeled by vector meson poles. We compute the peripheral charge and magnetization densities in the octet baryon states, estimate the uncertainties, and determine the quark flavor decomposition. Finally, the approach can be extended to baryon form factors of other operators and the moments of generalized parton distributions.« less

Effect of short-range correlations on the single proton 3s1/2 wave function in 206Pb

NASA Astrophysics Data System (ADS)

Shlomo, S.; Talmi, I.; Anders, M. R.; Bonasera, G.

2018-02-01

We consider the experimental data for difference, Δρc (r), between the charge density distributions of the isotones 206Pb - 205Tl, deduced by analysis of elastic electron scattering measurements and corresponds to the shell model 3s1/2 proton orbit. We investigate the effects of two-body short-range correlations. This is done by: (a) Determining the corresponding single particle potential (mean-field), employing a novel method, directly from the single particle proton density and its first and second derivatives. We also carried out least-square fits to parametrized single particle potentials; (b) Determining the short-range correlations effect by employing the Jastrow correlated many-body wave function to derive a correlation factor for the single particle density distribution. The 3s 1/2 wave functions of the determined potentials reproduce fairly well the experimental data within the quoted errors. The calculated charge density difference, Δρc (r), obtained with the inclusion of the short-range correlation effect does not reproduce the experimental data.

Approximate solution for the electronic density profile at the surface of jellium

NASA Astrophysics Data System (ADS)

Schmickler, Wolfgang; Henderson, Douglas

1984-09-01

A simple family of trial functions for the electronic density at the surface of jellium, which accounts for Friedel oscillations and incorporates the Budd-Vannimenus theorem, is proposed. The free parameters are determined by energy minimization. Model calculations give good results for the work function and for the induced surface charge in the presence of an external field.

The Poisson-Boltzmann theory for the two-plates problem: some exact results.

PubMed

Xing, Xiang-Jun

2011-12-01

The general solution to the nonlinear Poisson-Boltzmann equation for two parallel charged plates, either inside a symmetric electrolyte, or inside a 2q:-q asymmetric electrolyte, is found in terms of Weierstrass elliptic functions. From this we derive some exact asymptotic results for the interaction between charged plates, as well as the exact form of the renormalized surface charge density.

Testing time-dependent density functional theory with depopulated molecular orbitals for predicting electronic excitation energies of valence, Rydberg, and charge-transfer states and potential energies near a conical intersection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Shaohong L.; Truhlar, Donald G., E-mail: truhlar@umn.edu

2014-09-14

Kohn-Sham (KS) time-dependent density functional theory (TDDFT) with most exchange-correlation functionals is well known to systematically underestimate the excitation energies of Rydberg and charge-transfer excited states of atomic and molecular systems. To improve the description of Rydberg states within the KS TDDFT framework, Gaiduk et al. [Phys. Rev. Lett. 108, 253005 (2012)] proposed a scheme that may be called HOMO depopulation. In this study, we tested this scheme on an extensive dataset of valence and Rydberg excitation energies of various atoms, ions, and molecules. It is also tested on a charge-transfer excitation of NH{sub 3}-F{sub 2} and on the potentialmore » energy curves of NH{sub 3} near a conical intersection. We found that the method can indeed significantly improve the accuracy of predicted Rydberg excitation energies while preserving reasonable accuracy for valence excitation energies. However, it does not appear to improve the description of charge-transfer excitations that are severely underestimated by standard KS TDDFT with conventional exchange-correlation functionals, nor does it perform appreciably better than standard TDDFT for the calculation of potential energy surfaces.« less

Reformulated space-charge-limited current model and its application to disordered organic systems

NASA Astrophysics Data System (ADS)

Woellner, Cristiano F.; Freire, José A.

2011-02-01

We have reformulated a traditional model used to describe the current-voltage dependence of low mobility materials sandwiched between planar electrodes by using the quasi-electrochemical potential as the fundamental variable instead of the local electric field or the local charge carrier density. This allows the material density-of-states to enter explicitly in the equations and dispenses with the need to assume a particular type of contact. The diffusion current is included and as a consequence the current-voltage dependence obtained covers, with increasing bias, the diffusion limited current, the space-charge limited current, and the injection limited current regimes. The generalized Einstein relation and the field and density dependent mobility are naturally incorporated into the formalism; these two points being of particular relevance for disordered organic semiconductors. The reformulated model can be applied to any material where the carrier density and the mobility may be written as a function of the quasi-electrochemical potential. We applied it to the textbook example of a nondegenerate, constant mobility material and showed how a single dimensionless parameter determines the form of the I(V) curve. We obtained integral expressions for the carrier density and for the mobility as a function of the quasi-electrochemical potential for a Gaussianly disordered organic material and found the general form of the I(V) curve for such materials over the full range of bias, showing how the energetic disorder alone can give rise, in the space-charge limited current regime, to an I∝Vn dependence with an exponent n larger than 2.

Adsorption and Dissociation of Molecular Hydrogen on the (0001) Surface of DHCP Americium

NASA Astrophysics Data System (ADS)

Dholabhai, Pratik; Ray, Asok

2009-03-01

Hydrogen molecule adsorption on the (0001) surface of double hexagonal closed packed americium has been studied in detail within the framework of density functional theory. Weak molecular hydrogen adsorptions were observed. The most stable configuration corresponded to a Hor2 approach molecular adsorption at the one-fold top site where the molecule's approach is perpendicular to a lattice vector. Adsorption energies and adsorption geometries for different adsorption sites will be discussed. The change in work functions, magnetic moments, partial charges inside muffin-tins, difference charge density distributions and density of states for the bare Am slab and the Am slab after adsorption of the hydrogen molecule will be discussed. Reaction barrier for the dissociation of hydrogen molecule will be presented. The implications of adsorption on Am 5f electron localization-delocalization will be summarized.

Beam energy dependence of pseudorapidity distributions of charged particles produced in relativistic heavy-ion collisions

NASA Astrophysics Data System (ADS)

Basu, Sumit; Nayak, Tapan K.; Datta, Kaustuv

2016-06-01

Heavy-ion collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory and the Large Hadron Collider at CERN probe matter at extreme conditions of temperature and energy density. Most of the global properties of the collisions can be extracted from the measurements of charged-particle multiplicity and pseudorapidity (η ) distributions. We have shown that the available experimental data on beam energy and centrality dependence of η distributions in heavy-ion (Au +Au or Pb +Pb ) collisions from √{sNN}=7.7 GeV to 2.76 TeV are reasonably well described by the AMPT model, which is used for further exploration. The nature of the η distributions has been described by a double Gaussian function using a set of fit parameters, which exhibit a regular pattern as a function of beam energy. By extrapolating the parameters to a higher energy of √{sNN}=5.02 TeV, we have obtained the charged-particle multiplicity densities, η distributions, and energy densities for various centralities. Incidentally, these results match well with some of the recently published data by the ALICE Collaboration.

Covalent surface modification of chemically derived graphene and its application as supercapacitor electrode material.

PubMed

Jana, Milan; Khanra, Partha; Murmu, Naresh Chandra; Samanta, Pranab; Lee, Joong Hee; Kuila, Tapas

2014-04-28

A simple and effective method using 6-amino-4-hydroxy-2-naphthalenesulfonic acid (ANS) for the synthesis of water dispersible graphene has been described. Ultraviolet-visible (UV-vis) spectroscopy reveals that ANS-modified reduced graphene oxide (ANS-rGO) obeys Beers law at moderate concentrations. Fourier transform infrared and X-ray photoelectron spectroscopies provide quantitative information regarding the removal of oxygen functional groups from graphene oxide (GO) and the appearance of new functionalities in ANS-rGO. The electrochemical performances of ANS-rGO have been determined by cyclic voltammetry, charge-discharge and electrochemical impedance spectroscopy analysis. Charge-discharge experiments show that ANS-rGO is an outstanding supercapacitor electrode material due to its high specific capacitance (375 F g(-1) at a current density of 1.3 A g(-1)) and very good electrochemical cyclic stability (∼97.5% retention in specific capacitance after 1000 charge-discharge cycles). ANS-rGO exhibits promising characteristics with a very high power density (1328 W kg(-1)) and energy density (213 W h kg(-1)).

Thiophenic compounds adsorption on Na(I)Y and rare earth exchanged Y zeolites: a density functional theory study.

PubMed

Gao, Xionghou; Geng, Wei; Zhang, Haitao; Zhao, Xuefei; Yao, Xiaojun

2013-11-01

We have theoretically investigated the adsorption of thiophene, benzothiophene, dibenzothiophene on Na(I)Y and rare earth exchanged La(III)Y, Ce(III)Y, Pr(III)Y Nd(III)Y zeolites by density functional theory calculations. The calculated results show that except benzothiophene adsorbed on Na(I)Y with a stand configuration, the stable adsorption structures of other thiophenic compounds on zeolites exhibit lying configurations. Adsorption energies of thiophenic compounds on the Na(I)Y are very low, and decrease with the increase of the number of benzene rings in thiophenic compounds. All rare earth exchanged zeolites exhibit strong interaction with thiophene. La(III)Y and Nd(III)Y zeolites are found to show enhanced adsorption energies to benzothiophene and Pr(III)Y zeolites are favorable for dibenzothiophene adsorption. The analysis of the electronic total charge density and electron orbital overlaps show that the thiophenic compounds interact with zeolites by π-electrons of thiophene ring and exchanged metal atom. Mulliken charge populations analysis reveals that adsorption energies are strongly dependent on the charge transfer of thiophenic molecule and exchanged metal atom.

A theoretical study of structural and electronic properties of pentacene/Al(100) interface.

PubMed

Saranya, G; Nair, Shiny; Natarajan, V; Kolandaivel, P; Senthilkumar, K

2012-09-01

The first principle calculations within the framework of density functional theory have been performed for the pentacene molecule deposited on the aluminum Al(100) substrate to study the structural and electronic properties of the pentacene/Al(100) interface. The most stable configuration was found at bridge site with 45° rotation of the pentacene molecule on Al(100) surface with a vertical distance of 3.4 Å within LDA and 3.8 Å within GGA functionals. The calculated adsorption energy reveals that the adsorption of pentacene molecule on Al(100) surface is physisorption. For the stable adsorption geometry the electronic properties such as density of states (DOS), partial density of states (PDOS), Mulliken population analysis and Schottky barrier height are studied. The analysis of atomic charge, DOS and PDOS show that the charge is transferred from the Al(100) surface to pentacene molecule, and the transferred charge is about -0.05 electrons. For the adsorbed system, the calculated Schottky barrier height for hole and electron transport is 0.27 and 1.55 eV, respectively. Copyright © 2012 Elsevier Inc. All rights reserved.

The dielectric function of weakly ionized dusty plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Hui; China Research Institute of Radio wave Propagation; Wu, Jian

2016-07-15

Using classical Boltzmann kinetic theory, the dielectric function of weakly ionized unmagnetized dusty plasma is derived. The elastic Coulomb collision and inelastic charging collision of electrons with charged dust particle as well as charge variation on dust surface are taken into account. The theoretical result is applied to analyze the propagation of electromagnetic wave in a dusty plasma. It is demonstrated that the additional collision mechanism provided by charged dust particle can significantly increase the absorbed power of electromagnetic wave. These increases are mainly determined by the dust radius, density, and the charge numbers on the dust surface. The obtainedmore » results will support an enhanced understanding of the wave propagation processes in space and laboratory dusty plasmas.« less

An accurate and linear-scaling method for calculating charge-transfer excitation energies and diabatic couplings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavanello, Michele; Van Voorhis, Troy; Visscher, Lucas

2013-02-07

Quantum-mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this goal for those charge transfer excitations that take place between non-covalently bound molecules. In particular, we present a method that scales linearly with the number of non-covalently bound molecules in the system and is based on a two-pronged approach: The molecular electronic structure of broken-symmetry charge-localized states is obtained with the frozen density embedding formulation of subsystem density-functional theory; subsequently, in a post-SCF calculation, the full-electron Hamiltonian and overlapmore » matrix elements among the charge-localized states are evaluated with an algorithm which takes full advantage of the subsystem DFT density partitioning technique. The method is benchmarked against coupled-cluster calculations and achieves chemical accuracy for the systems considered for intermolecular separations ranging from hydrogen-bond distances to tens of Angstroms. Numerical examples are provided for molecular clusters comprised of up to 56 non-covalently bound molecules.« less

An accurate and linear-scaling method for calculating charge-transfer excitation energies and diabatic couplings.

PubMed

Pavanello, Michele; Van Voorhis, Troy; Visscher, Lucas; Neugebauer, Johannes

2013-02-07

Quantum-mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this goal for those charge transfer excitations that take place between non-covalently bound molecules. In particular, we present a method that scales linearly with the number of non-covalently bound molecules in the system and is based on a two-pronged approach: The molecular electronic structure of broken-symmetry charge-localized states is obtained with the frozen density embedding formulation of subsystem density-functional theory; subsequently, in a post-SCF calculation, the full-electron Hamiltonian and overlap matrix elements among the charge-localized states are evaluated with an algorithm which takes full advantage of the subsystem DFT density partitioning technique. The method is benchmarked against coupled-cluster calculations and achieves chemical accuracy for the systems considered for intermolecular separations ranging from hydrogen-bond distances to tens of Ångstroms. Numerical examples are provided for molecular clusters comprised of up to 56 non-covalently bound molecules.

Photoelectron Spectroscopy of Doubly and Singly Charged Group VIB Dimetalate Anions: M2O72-, MM'072-, and M207- (M, M'=Cr, Mo, W)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhai, Hua Jin; Huang, Xin; Waters, Tom

2005-11-24

We produced both doubly and singly charged Group VIB dimetalate species-M2O7 2-, MM'O72-, and M2O7 - (M, M'=) Cr, Mo, W)susing two different experimental techniques (electrospray ionization for the doubly charged anions and laser vaporization for the singly charged anions) and investigated their electronic and geometric structures using photoelectron spectroscopy and density functional calculations. Distinct changes in the electronic and geometric structures were observed as a function of the metal and charge state. The electron binding energies of the heteronuclear dianions MM'O7 2- were observed to be roughly the average of those of their homonuclear counterparts (M2O7 2- and M'2O7more » 2-). Density functional calculations indicated that W2O7 2-, W2O7-, and W2O7 possess different ground-state structures: the dianion is highly symmetric (D3d,1A1g) with a single bridging oxo ligand, the monoanion is a doublet (C1, 2A) with two bridging oxo ligands and a radical terminal oxo ligand, whereas the neutral is a singlet (C1, 1A) with two bridging oxo ligands and a terminal peroxo ligand. The combined experimental and theoretical study provides insights into the evolution of geometric and electronic structures as a function of charge state. The clusters identified might provide insights into the possible structures of reactive species present in early transition-metal oxide catalysts that are relevant to their reactivity and catalytic function.« less

Central charge from adiabatic transport of cusp singularities in the quantum Hall effect

NASA Astrophysics Data System (ADS)

Can, Tankut

2017-04-01

We study quantum Hall (QH) states on a punctured Riemann sphere. We compute the Berry curvature under adiabatic motion in the moduli space in the large N limit. The Berry curvature is shown to be finite in the large N limit and controlled by the conformal dimension of the cusp singularity, a local property of the mean density. Utilizing exact sum rules obtained from a Ward identity, we show that for the Laughlin wave function, the dimension of a cusp singularity is given by the central charge, a robust geometric response coefficient in the QHE. Thus, adiabatic transport of curvature singularities can be used to determine the central charge of QH states. We also consider the effects of threaded fluxes and spin-deformed wave functions. Finally, we give a closed expression for all moments of the mean density in the integer QH state on a punctured disk.

Theoretical study of the Raman active CDW gap mode in manganites.

PubMed

Rout, G C; Panda, Saswati; Behera, S N

2010-09-22

We report here the microscopic theory of the Raman spectra of the colossal magnetoresistive (CMR) manganite systems. The system is described by a model Hamiltonian consisting of the double exchange interaction in addition to the charge ordering interaction in the e(g) band and spin-spin interaction among the t(2g) core electrons. Further the phonon coupling to the conduction electron density is incorporated in the model for phonons in the harmonic approximation. The spectral density function for the Raman spectra is calculated from the imaginary part of the phonon Green's function. The calculated spectra display the Raman active bare phonon peak along with the charge ordering peak. The magnetic field and temperature dependence of the charge ordering peak agrees with the 480 cm(-1) JT mode observed in the experiments. The evolution of this mode is investigated in the report.

Role of Surface Charge Density in Nanoparticle-templated Assembly of Bromovirus Protein Cages

PubMed Central

Daniel, Marie-Christine; Tsvetkova, Irina B.; Quinkert, Zachary T.; Murali, Ayaluru; De, Mrinmoy; Rotello, Vincent M.; Kao, C. Cheng; Dragnea, Bogdan

2010-01-01

Self-assembling icosahedral protein cages have potencially useful physical and chemical characteristics for a variety of nanotechnology applications, ranging from therapeutic or diagnostic vectors to building blocks for hierarchical materials. For application-specific functional control of protein cage assemblies, a deeper understanding of the interaction between the protein cage and its payload is necessary. Protein-cage encapsulated nanoparticles, with their well-defined surface chemistry, allow for systematic control over key parameters of encapsulation such as the surface charge, hydrophobicity, and size. Independent control over these variables allows experimental testing of different assembly mechanism models. Previous studies done with Brome mosaic virus capsids and negatively-charged gold nanoparticles indicated that the result of the self-assembly process depends on the diameter of the particle. However, in these experiments, the surface-ligand density was maintained at saturation levels, while the total charge and the radius of curvature remained coupled variables, making the interpretation of the observed dependence on the core size difficult. The current work furnishes evidence of a critical surface charge density for assembly through an analysis aimed at decoupling the surface charge the core size. PMID:20575505

Functional adaptation between yeast actin and its cognate myosin motors.

PubMed

Stark, Benjamin C; Wen, Kuo-Kuang; Allingham, John S; Rubenstein, Peter A; Lord, Matthew

2011-09-02

We employed budding yeast and skeletal muscle actin to examine the contribution of the actin isoform to myosin motor function. While yeast and muscle actin are highly homologous, they exhibit different charge density at their N termini (a proposed myosin-binding interface). Muscle myosin-II actin-activated ATPase activity is significantly higher with muscle versus yeast actin. Whether this reflects inefficiency in the ability of yeast actin to activate myosin is not known. Here we optimized the isolation of two yeast myosins to assess actin function in a homogenous system. Yeast myosin-II (Myo1p) and myosin-V (Myo2p) accommodate the reduced N-terminal charge density of yeast actin, showing greater activity with yeast over muscle actin. Increasing the number of negative charges at the N terminus of yeast actin from two to four (as in muscle) had little effect on yeast myosin activity, while other substitutions of charged residues at the myosin interface of yeast actin reduced activity. Thus, yeast actin functions most effectively with its native myosins, which in part relies on associations mediated by its outer domain. Compared with yeast myosin-II and myosin-V, muscle myosin-II activity was very sensitive to salt. Collectively, our findings suggest differing degrees of reliance on electrostatic interactions during weak actomyosin binding in yeast versus muscle. Our study also highlights the importance of native actin isoforms when considering the function of myosins.

Molecular density functional theory of water including density-polarization coupling.

PubMed

Jeanmairet, Guillaume; Levy, Nicolas; Levesque, Maximilien; Borgis, Daniel

2016-06-22

We present a three-dimensional molecular density functional theory of water derived from first-principles that relies on the particle's density and multipolar polarization density and includes the density-polarization coupling. This brings two main benefits: (i) scalar density and vectorial multipolar polarization density fields are much more tractable and give more physical insight than the full position and orientation densities, and (ii) it includes the full density-polarization coupling of water, that is known to be non-vanishing but has never been taken into account. Furthermore, the theory requires only the partial charge distribution of a water molecule and three measurable bulk properties, namely the structure factor and the Fourier components of the longitudinal and transverse dielectric susceptibilities.

Liquid Drop Model for Charged Spherical Metal Clusters

NASA Astrophysics Data System (ADS)

Seidl, M.; Brack, M.

1996-02-01

The average ground-state energy of a charged spherical metal cluster withNatoms andzexcessive valence electrons, i.e., with net chargeQ=-ezand radiusR=rsN1/3, is presented in the liquid drop model (LDM) expansionE(N, z)=avN+asN2/3+acN1/3+a0(z)+a-1(z) N-1/3+O(N-2/3). We derive analytical expressions for the leading LDM coefficientsav,as,ac, and, in particular, for the charge dependence of the further LDM coefficientsa0anda-1, using the jellium model and density functional theory in the local density approximation. We obtain for the ionization energyI(R)=W+α(e2/R)+O(R-2), with the bulk work functionW=[Φ(+∞)-Φ(0)]-eb, given first by Mahan and Schaich in terms of the electrostatic potentialΦand the bulk energy per electroneb, and a new analytical expression for the dimensionless coefficientα. We demonstrate that within classical theoryα={1}/{2} but, in agreement with experimental information,αtends to ∼0.4 if quantum-mechanical contributions are included. In order to test and confirm our analytical expressions, we discuss the numerical results of semiclassical density variational calculations in the extended Thomas-Fermi model.

Some modification of cellulose nanocrystals for functional Pickering emulsions

PubMed Central

Saidane, Dorra; Perrin, Emilie; Cherhal, Fanch; Guellec, Florian

2016-01-01

Cellulose nanocrystals (CNCs) are negatively charged colloidal particles well known to form highly stable surfactant-free Pickering emulsions. These particles can vary in surface charge density depending on their preparation by acid hydrolysis or applying post-treatments. CNCs with three different surface charge densities were prepared corresponding to 0.08, 0.16 and 0.64 e nm−2, respectively. Post-treatment might also increase the surface charge density. The well-known TEMPO-mediated oxidation substitutes C6-hydroxyl groups by C6-carboxyl groups on the surface. We report that these different modified CNCs lead to stable oil-in-water emulsions. TEMPO-oxidized CNC might be the basis of further modifications. It is shown that they can, for example, lead to hydrophobic CNCs with a simple method using quaternary ammonium salts that allow producing inverse water-in-oil emulsions. Different from CNC modification before emulsification, modification can be carried out on the droplets after emulsification. This way allows preparing functional capsules according to the layer-by-layer process. As a result, it is demonstrated here the large range of use of these biobased rod-like nanoparticles, extending therefore their potential use to highly sophisticated formulations. This article is part of the themed issue ‘Soft interfacial materials: from fundamentals to formulation’. PMID:27298429

Multiphoton ionization of many-electron atoms and highly-charged ions in intense laser fields: a relativistic time-dependent density functional theory approach

NASA Astrophysics Data System (ADS)

Tumakov, Dmitry A.; Telnov, Dmitry A.; Maltsev, Ilia A.; Plunien, Günter; Shabaev, Vladimir M.

2017-10-01

We develop an efficient numerical implementation of the relativistic time-dependent density functional theory (RTDDFT) to study multielectron highly-charged ions subject to intense linearly-polarized laser fields. The interaction with the electromagnetic field is described within the electric dipole approximation. The resulting time-dependent relativistic Kohn-Sham (RKS) equations possess an axial symmetry and are solved accurately and efficiently with the help of the time-dependent generalized pseudospectral method. As a case study, we calculate multiphoton ionization probabilities of the neutral argon atom and argon-like xenon ion. Relativistic effects are assessed by comparison of our present results with existing non-relativistic data.

Modulated two-dimensional charge-carrier density in LaTiO3-layer-doped LaAlO3/SrTiO3 heterostructure.

PubMed

Nazir, Safdar; Bernal, Camille; Yang, Kesong

2015-03-11

The highly mobile two-dimensional electron gas (2DEG) formed at the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) is a matter of great interest because of its potential applications in nanoscale solid-state devices. To realize practical implementation of the 2DEG in device design, desired physical properties such as tuned charge carrier density and mobility are necessary. In this regard, polar perovskite-based transition metal oxides can act as doping layers at the interface and are expected to tune the electronic properties of 2DEG of STO-based HS systems dramatically. Herein, we investigated the doping effects of LaTiO3(LTO) layers on the electronic properties of 2DEG at n-type (LaO)(+1)/(TiO2)(0) interface in the LAO/STO HS using spin-polarized density functional theory calculations. Our results indicate an enhancement of orbital occupation near the Fermi energy, which increases with respect to the number of LTO unit cells, resulting in a higher charge carrier density of 2DEG than that of undoped system. The enhanced charge carrier density is attributed to an extra electron introduced by the Ti 3d(1) orbitals from the LTO dopant unit cells. This conclusion is consistent with the recent experimental findings (Appl. Phys. Lett. 2013, 102, 091601). Detailed charge density and partial density of states analysis suggests that the 2DEG in the LTO-doped HS systems primarily comes from partially occupied dyz and dxz orbitals.

F4TCNQ on Cu, Ag, and Au as prototypical example for a strong organic acceptor on coinage metals

NASA Astrophysics Data System (ADS)

Rangger, Gerold M.; Hofmann, Oliver T.; Romaner, Lorenz; Heimel, Georg; Bröker, Benjamin; Blum, Ralf-Peter; Johnson, Robert L.; Koch, Norbert; Zojer, Egbert

2009-04-01

Metal work-function modification with the help of organic acceptors is an efficient tool to significantly enhance the performance of modern state-of-the-art organic molecular electronic devices. Here, the prototypical organic acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, F4TCNQ, is characterized on Ag(111), Au(111), and Cu(111) metal surfaces by means of density-functional theory calculations. Particular attention is paid to charge-transfer processes at the metal-organic interface; a subtle balance between charge forward and backward donations in combination with a strong adsorption-induced geometry change are found to be responsible for the observed increase in the system work function. A larger effect is obtained for the metals with larger initial work function. Interestingly, this results in similar charge-injection barriers from the substrate metal into an organic semiconductor deposited on top of the F4TCNQ layer. The impact of the F4TCNQ packing density of the electronic properties of the interface is also addressed. Comparing the calculated energy-level alignments and work-function modifications to experimental data from ultraviolet photoelectron spectroscopy yields good agreement between experiments and simulations.

Source-Free Exchange-Correlation Magnetic Fields in Density Functional Theory.

PubMed

Sharma, S; Gross, E K U; Sanna, A; Dewhurst, J K

2018-03-13

Spin-dependent exchange-correlation energy functionals in use today depend on the charge density and the magnetization density: E xc [ρ, m]. However, it is also correct to define the functional in terms of the curl of m for physical external fields: E xc [ρ,∇ × m]. The exchange-correlation magnetic field, B xc , then becomes source-free. We study this variation of the theory by uniquely removing the source term from local and generalized gradient approximations to the functional. By doing so, the total Kohn-Sham moments are improved for a wide range of materials for both functionals. Significantly, the moments for the pnictides are now in good agreement with experiment. This source-free method is simple to implement in all existing density functional theory codes.

Theoretical investigation of discharge parameters in magnetized radio frequency excited CO2 lasers

NASA Astrophysics Data System (ADS)

Tavassoli, H.; Sohbatzadeh, F.; Latifi, H.

2003-06-01

In the present paper the magnetic field effects on discharge parameters in rf excited CO2 lasers are calculated. A rf generated plasma imbedded in an external, constant, and homogeneous magnetic field is considered. The continuity equation is used to derive the electron density. Quasineutrality condition and ambipolar diffusion are used. Electron attachment coefficient is neglected. Local electric field, local electron density, and thickness of charge layers are derived as a function of distance from the electrodes and magnetic field. The thickness of charge layers in the presence of magnetic field is always smaller than one without the magnetic field. When the magnetic field increases, the electron density increases in all regions of discharge, and the electric field reduces in the charge layers but increases in the middle part of discharge.

Impact of Many-Body Effects on Landau Levels in Graphene

NASA Astrophysics Data System (ADS)

Sonntag, J.; Reichardt, S.; Wirtz, L.; Beschoten, B.; Katsnelson, M. I.; Libisch, F.; Stampfer, C.

2018-05-01

We present magneto-Raman spectroscopy measurements on suspended graphene to investigate the charge carrier density-dependent electron-electron interaction in the presence of Landau levels. Utilizing gate-tunable magnetophonon resonances, we extract the charge carrier density dependence of the Landau level transition energies and the associated effective Fermi velocity vF. In contrast to the logarithmic divergence of vF at zero magnetic field, we find a piecewise linear scaling of vF as a function of the charge carrier density, due to a magnetic-field-induced suppression of the long-range Coulomb interaction. We quantitatively confirm our experimental findings by performing tight-binding calculations on the level of the Hartree-Fock approximation, which also allow us to estimate an excitonic binding energy of ≈6 meV contained in the experimentally extracted Landau level transitions energies.

Transcranial direct current stimulation in the male mouse to promote recovery after stroke.

PubMed

Pikhovych, Anton; Walter, Helene L; Mahabir, Esther; Fink, Gereon Rudolf; Graf, Rudolf; Schroeter, Michael; Rueger, Maria Adele

2016-06-01

Transcranial direct current stimulation (tDCS) constitutes a promising approach for promoting recovery of function after stroke, although the underlying neurobiological mechanisms are unclear. To conduct translational research in animal models, stimulation parameters should not lead to neuronal lesions. Liebetanz et al. recommend charge densities for cathodal stimulation in rats, but parameters for mice are not established. We established tDCS in the wild-type mouse, enabling studies with genetically-engineered mice (GEM). tDCS equipment was adapted to fit the mouse skull. Using different polarities and charge densities, tDCS was safe to apply in the mouse where the charge density was below 198 kC/m(2) for single or repeated stimulations. These findings are crucial for future investigations of the neurobiological mechanisms underlying tDCS using GEM. © The Author(s) 2015.

Stability of Li- and Mn-Rich Layered-Oxide Cathodes within the First-Charge Voltage Plateau

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iddir, Hakim; Bareño, Javier; Benedek, Roy

Li and Mn rich layered oxides xLi 2MnO 3•(1-x)LiMO 2 enable high capacity and energy density Li-ion batteries, but undergo structural transformations during the first charge that degrade their performance, and result in Voltage Fade upon cycling. First-principles density-functional-theory simulations reveal atomic transformations that occur in the bulk during the first charge. The simulations and experiment (particularly XRD) show that the O and Mn sublattices remain intact during the early part of the voltage plateau, and significant transformations occur only well into the voltage plateau, with perhaps close to half of the Li in the Li 2MnO 3 domains removed.more » That Voltage Fade is actually observed experimentally for a first charge with only minimal activation (extending only slightly beyond the onset of the voltage plateau) may be a consequence of surface and interface instabilities. Implications for the achievement of high energy-density, low-fade battery operation are discussed.« less

Diffusive charge transport in graphene on SiO 2

NASA Astrophysics Data System (ADS)

Chen, J.-H.; Jang, C.; Ishigami, M.; Xiao, S.; Cullen, W. G.; Williams, E. D.; Fuhrer, M. S.

2009-07-01

We review our recent work on the physical mechanisms limiting the mobility of graphene on SiO 2. We have used intentional addition of charged scattering impurities and systematic variation of the dielectric environment to differentiate the effects of charged impurities and short-range scatterers. The results show that charged impurities indeed lead to a conductivity linear in density ( σ(n)∝n) in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates; increased dielectric screening reduces the scattering from charged impurities, but increases the scattering from short-range scatterers. We evaluate the effects of the corrugations (ripples) of graphene on SiO 2 on transport by measuring the height-height correlation function. The results show that the corrugations cannot mimic long-range (charged impurity) scattering effects, and have too small an amplitude-to-wavelength ratio to significantly affect the observed mobility via short-range scattering. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a resistivity that is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO 2 substrate give rise to an activated, carrier density-dependent resistivity. Together the results paint a complete picture of charge carrier transport in graphene on SiO 2 in the diffusive regime.

Charge states of ions, and mechanisms of charge ordering transitions

NASA Astrophysics Data System (ADS)

Pickett, Warren E.; Quan, Yundi; Pardo, Victor

2014-07-01

To gain insight into the mechanism of charge ordering transitions, which conventionally are pictured as a disproportionation of an ion M as 2Mn+→M(n+1)+ + M(n-1)+, we (1) review and reconsider the charge state (or oxidation number) picture itself, (2) introduce new results for the putative charge ordering compound AgNiO2 and the dual charge state insulator AgO, and (3) analyze the cationic occupations of the actual (not formal) charge, and work to reconcile the conundrums that arise. We establish that several of the clearest cases of charge ordering transitions involve no disproportion (no charge transfer between the cations, and hence no charge ordering), and that the experimental data used to support charge ordering can be accounted for within density functional-based calculations that contain no charge transfer between cations. We propose that the charge state picture retains meaning and importance, at least in many cases, if one focuses on Wannier functions rather than atomic orbitals. The challenge of modeling charge ordering transitions with model Hamiltonians isdiscussed.

Structures, phase stabilities, and electrical potentials of Li-Si battery anode materials

NASA Astrophysics Data System (ADS)

Tipton, William W.; Bealing, Clive R.; Mathew, Kiran; Hennig, Richard G.

2013-05-01

The Li-Si materials system holds promise for use as an anode in Li-ion battery applications. For this system, we determine the charge capacity, voltage profiles, and energy storage density solely by ab initio methods without any experimental input. We determine the energetics of the stable and metastable Li-Si phases likely to form during the charging and discharging of a battery. Ab initio molecular dynamics simulations are used to model the structure of amorphous Li-Si as a function of composition, and a genetic algorithm coupled to density-functional theory searches the Li-Si binary phase diagram for small-cell, metastable crystal structures. Calculations of the phonon densities of states using density-functional perturbation theory for selected structures determine the importance of vibrational, including zero-point, contributions to the free energies. The energetics and local structural motifs of these metastable Li-Si phases closely resemble those of the amorphous phases, making these small unit cell crystal phases good approximants of the amorphous phase for use in further studies. The charge capacity is estimated, and the electrical potential profiles and the energy density of Li-Si anodes are predicted. We find, in good agreement with experimental measurements, that the formation of amorphous Li-Si only slightly increases the anode potential. Additionally, the genetic algorithm identifies a previously unreported member of the Li-Si binary phase diagram with composition Li5Si2 which is stable at 0 K with respect to previously known phases. We discuss its relationship to the partially occupied Li7Si3 phase.

Simulation of electric double-layer capacitors: evaluation of constant potential method

NASA Astrophysics Data System (ADS)

Wang, Zhenxing; Laird, Brian; Yang, Yang; Olmsted, David; Asta, Mark

2014-03-01

Atomistic simulations can play an important role in understanding electric double-layer capacitors (EDLCs) at a molecular level. In such simulations, typically the electrode surface is modeled using fixed surface charges, which ignores the charge fluctuation induced by local fluctuations in the electrolyte solution. In this work we evaluate an explicit treatment of charges, namely constant potential method (CPM)[1], in which the electrode charges are dynamically updated to maintain constant electrode potential. We employ a model system with a graphite electrode and a LiClO4/acetonitrile electrolyte, examined as a function of electrode potential differences. Using various molecular and macroscopic properties as metrics, we compare CPM simulations on this system to results using fixed surface charges. Specifically, results for predicted capacity, electric potential gradient and solvent density profile are identical between the two methods; However, ion density profiles and solvation structure yield significantly different results.

Electron density modification in ionospheric E layer by inserting fine dust particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Misra, Shikha, E-mail: shikhamish@gmail.com; Mishra, S. K.

2015-02-15

In this paper, we have developed the kinetics of E-region ionospheric plasma comprising of fine dust grains and shown that the electron density in E-layer can purposely be reduced/enhanced up to desired level by inserting fine dust particles of appropriate physical/material properties; this may certainly be promising for preferred rf-signal processing through these layers. The analytical formulation is based on average charge theory and includes the number and energy balance of the plasma constituents along with charge balance over dust particles. The effect of varying number density, work function, and photo-efficiency of dust particles on ionospheric plasma density at differentmore » altitude in E-layer has been critically examined and presented graphically.« less

Communication: Two-step explosion processes of highly charged fullerene cations C{sub 60}{sup q+} (q = 20–60)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamazaki, Kaoru; Nakamura, Takashi; Kanno, Manabu

2014-09-28

To establish the fundamental understanding of the fragmentation dynamics of highly positive charged nano- and bio-materials, we carried out on-the-fly classical trajectory calculations on the fragmentation dynamics of C{sub 60}{sup q+} (q = 20–60). We used the UB3LYP/3-21G level of density functional theory and the self-consistent charge density-functional based tight-binding theory. For q ≥ 20, we found that a two-step explosion mechanism governs the fragmentation dynamics: C{sub 60}{sup q+} first ejects singly and multiply charged fast atomic cations C{sup z+} (z ≥ 1) via Coulomb explosions on a timescale of 10 fs to stabilize the remaining core cluster. Thermal evaporationsmore » of slow atomic and molecular fragments from the core cluster subsequently occur on a timescale of 100 fs to 1 ps. Increasing the charge q makes the fragments smaller. This two-step mechanism governs the fragmentation dynamics in the most likely case that the initial kinetic energy accumulated upon ionization to C{sub 60}{sup q+} by ion impact or X-ray free electron laser is larger than 100 eV.« less

Negative Differential Conductance in Polyporphyrin Oligomers with Nonlinear Backbones.

PubMed

Kuang, Guowen; Chen, Shi Zhang; Yan, Linghao; Chen, Ke Qiu; Shang, Xuesong; Liu, Pei Nian; Lin, Nian

2018-01-17

We study negative differential conductance (NDC) effects in polyporphyrin oligomers with nonlinear backbones. Using a low-temperature scanning tunneling microscope, we selectively controlled the charge transport path in single oligomer wires. We observed robust NDC when charge passed through a T-shape junction, bistable NDC when charge passed through a 90° kink and no NDC when charge passed through a 120° kink. Aided by density functional theory with nonequilibrium Green's functions simulations, we attributed this backbone-dependent NDC to bias-modulated hybridization of the electrode states with the resonant transport molecular orbital. We argue this mechanism is generic in molecular systems, which opens a new route of designing molecular NDC devices.

Charge transfer in iridate-manganite superlattices

DOE PAGES

Okamoto, Satoshi; Nichols, John; Sohn, Changhee; ...

2017-03-03

Charge transfer in superlattices consisting of SrIrOmore » $$_3$$ and SrMnO$$_3$$ is investigated using density functional theory. Despite the nearly identical work function and non-polar interfaces between SrIrO$$_3$$ and SrMnO$$_3$$, rather large charge transfer was experimentally reported between them. Our results provide a qualitative understanding to such experimental reports. We further develop a microscopic model that captures the mechanism behind this phenomenon. This leads to unique strain dependence of such charge transfer in iridate-manganite superlattices. The predicted behavior is consistently verified by experiment. Lastly, our work thus demonstrates a new route to control electronic states in non-polar oxide heterostructures.« less

Centrality dependence of charged particle multiplicity at midrapidity in Au+Au collisions at (sNN)=130 GeV

NASA Astrophysics Data System (ADS)

Back, B. B.; Baker, M. D.; Barton, D. S.; Betts, R. R.; Bindel, R.; Budzanowski, A.; Busza, W.; Carroll, A.; Decowski, M. P.; Garcia, E.; George, N.; Gulbrandsen, K.; Gushue, S.; Halliwell, C.; Heintzelman, G. A.; Henderson, C.; Hołyński, R.; Hofman, D. J.; Holzman, B.; Johnson, E.; Kane, J. L.; Katzy, J.; Khan, N.; Kucewicz, W.; Kulinich, P.; Lin, W. T.; Manly, S.; McLeod, D.; Michałowski, J.; Mignerey, A. C.; Mülmenstädt, J.; Nouicer, R.; Olszewski, A.; Pak, R.; Park, I. C.; Pernegger, H.; Reed, C.; Remsberg, L. P.; Reuter, M.; Roland, C.; Roland, G.; Rosenberg, L.; Sarin, P.; Sawicki, P.; Skulski, W.; Steadman, S. G.; Stephans, G. S.; Steinberg, P.; Stodulski, M.; Sukhanov, A.; Tang, J.-L.; Teng, R.; Trzupek, A.; Vale, C.; van Nieuwenhuizen, G. J.; Verdier, R.; Wadsworth, B.; Wolfs, F. L.; Wosiek, B.; Woźniak, K.; Wuosmaa, A. H.; Wysłouch, B.

2002-03-01

We present a measurement of the pseudorapidity density of primary charged particles near midrapidity in Au+Au collisions at (sNN)=130 GeV as a function of the number of participating nucleons. The pseudorapidity density, dNch/dη\\|\\|η\\|<1/(1/2), rises from 2.87+/-0.21 in peripheral events (~83) to 3.45+/-0.18 in central events (~353), which is 53+/-8% higher than pp&; collisions at a similar center-of-mass energy. This is consistent with an additional contribution to charged particle production that scales with the number of binary nucleon-nucleon collisions (Ncoll).

Theoretical characterization and design of small molecule donor material containing naphthodithiophene central unit for efficient organic solar cells.

PubMed

Duan, Yu-Ai; Geng, Yun; Li, Hai-Bin; Jin, Jun-Ling; Wu, Yong; Su, Zhong-Min

2013-07-15

To seek for high-performance small molecule donor materials used in heterojunction solar cell, six acceptor-donor-acceptor small molecules based on naphtho[2,3-b:6,7-b']dithiophene (NDT) units with different acceptor units were designed and characterized using density functional theory and time-dependent density functional theory. Their geometries, electronic structures, photophysical, and charge transport properties have been scrutinized comparing with the reported donor material NDT(TDPP)2 (TDPP  =  thiophene-capped diketopyrrolopyrrole). The open circuit voltage (V(oc)), energetic driving force(ΔE(L-L)), and exciton binding energy (E(b)) were also provided to give an elementary understanding on their cell performance. The results reveal that the frontier molecular orbitals of 3-7 match well with the acceptor material PC61 BM, and compounds 3-5 were found to exhibit the comparable performances to 1 and show promising potential in organic solar cells. In particular, comparing with 1, system 7 with naphthobisthiadiazole acceptor unit displays broader absorption spectrum, higher V(oc), lower E(b), and similar carrier mobility. An in-depth insight into the nature of the involved excited states based on transition density matrix and charge density difference indicates that all S1 states are mainly intramolecular charge transfer states with the charge transfer from central NDT unit to bilateral acceptor units, and also imply that the exciton of 7 can be dissociated easily due to its large extent of the charge transfer. In a word, 7 maybe superior to 1 and may act as a promising donor candidate for organic solar cell. Copyright © 2013 Wiley Periodicals, Inc.

Charge Injection Capacity of TiN Electrodes for an Extended Voltage Range

PubMed Central

Patan, Mustafa; Shah, Tosha; Sahin, Mesut

2011-01-01

Many applications of neural stimulation demand a high current density from the electrodes used for stimulus delivery. New materials have been searched that can provide such large current and charge densities where the traditional noble metal and capacitor electrodes are inadequate. Titanium nitride, which has been used in cardiac pacemaker leads for many years, is one of these materials recently considered for neural stimulation. In this short report, we investigated the charge injection capacity of TiN electrodes for an extended range of cathodic voltages. The injected charge increased first slowly as a function of the electrode voltage, and then at a faster rate beyond −1.6 V. The maximum charge was 4.45 mC/cm2 (n=6) for a cathodic voltage peak of −3.0 V and a bias voltage of −0.8 V. There was no evidence of bubble generation under microscopic observation. The unrecoverable charges remained under 7% of the total injected charge for the largest cathodic voltage tested. These large values of charge injection capacity and relatively small unrecoverable charges warrant further investigation of the charge injection mechanism in TiN interfaces at this extended range of electrode voltages. PMID:17946870

Nuclear longitudinal form factors for axially deformed charge distributions expanded by nonorthogonal basis functions

NASA Astrophysics Data System (ADS)

Liu, Jian; Zhang, Jinjuan; Xu, Chang; Ren, Zhongzhou

2017-05-01

In this paper, the nuclear longitudinal form factors are systematically studied from the intrinsic charge multipoles. For axially deformed nuclei, two different types of density profiles are used to describe their charge distributions. For the same charge distributions expanded with different basis functions, the corresponding longitudinal form factors are derived and compared with each other. Results show the multipoles Cλ of longitudinal form factors are independent of the basis functions of charge distributions. Further numerical calculations of longitudinal form factors of 12C indicates that the C 0 multipole reflects the contributions of spherical components of all nonorthogonal basis functions. For deformed nuclei, their charge RMS radii can also be determined accurately by the C 0 measurement. The studies in this paper examine the model-independent properties of electron scattering, which are useful for interpreting electron scattering experiments on exotic deformed nuclei. Supported by National Natural Science Foundation of China (11505292, 11175085, 11575082, 11235001, 11275138, and 11447226), by Shandong Provincial Natural Science Foundation, China (BS2014SF007), Fundamental Research Funds for Central Universities (15CX02072A).

Charge localization and ordering in A 2 Mn 8 O 16 hollandite group oxides: Impact of density functional theory approaches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaltak, Merzuk; Fernandez-Serra, Marivi; Hybertsen, Mark S.

The phases of A 2Mn 8O 16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3d electrons are more explicitly considered with the DFT + Umore » approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn 3+ centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Lastly, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.« less

Charge localization and ordering in A 2 Mn 8 O 16 hollandite group oxides: Impact of density functional theory approaches

DOE PAGES

Kaltak, Merzuk; Fernandez-Serra, Marivi; Hybertsen, Mark S.

2017-12-01

The phases of A 2Mn 8O 16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3d electrons are more explicitly considered with the DFT + Umore » approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn 3+ centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Lastly, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.« less

Charge localization and ordering in A2Mn8O16 hollandite group oxides: Impact of density functional theory approaches

NASA Astrophysics Data System (ADS)

Kaltak, Merzuk; Fernández-Serra, Marivi; Hybertsen, Mark S.

2017-12-01

The phases of A2Mn8O16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3 d electrons are more explicitly considered with the DFT + U approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn3 + centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Finally, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.

Effect of Temperature on Formation and Stability of Shallow Trap at a Dielectric Interface of the Multilayer

NASA Astrophysics Data System (ADS)

Rogti, F.

2015-12-01

Space-charge behavior at dielectric interfaces in multilayer low-density polyethylene (LDPE) and fluorinated ethylene propylene (FEP) subjected to a direct-current (DC) field has been investigated as a function of temperature using the pulsed electroacoustic technique. A sandwich structure constituted by two nonidentical LDPE/FEP dielectric films was used to study the charging propensity of electrode/dielectric and dielectric/dielectric interfaces. The time dependence of the space-charge distribution was subsequently recorded at four temperatures, 20°C, 25°C, 40°C, and 60°C, under field (polarization) and short-circuit (depolarization) conditions. The experimental results demonstrate that temperature plays a significant role in the space-charge dynamics at the dielectric interface. It affects the charge injection, increases the charge mobility and electrical conductivity, and increases the density of shallow traps and trap filling. It is found that traps formed during polarization at high temperature do not remain stable after complete discharge of the multidielectric structure and when poled at low temperatures.

A review of studies on ion thruster beam and charge-exchange plasmas

NASA Technical Reports Server (NTRS)

Carruth, M. R., Jr.

1982-01-01

Various experimental and analytical studies of the primary beam and charge-exchange plasmas of ion thrusters are reviewed. The history of plasma beam research is recounted, emphasizing experiments on beam neutralization, expansion of the beam, and determination of beam parameters such as electron temperature, plasma density, and plasma potential. The development of modern electron bombardment ion thrusters is treated, detailing experimental results. Studies on charge-exchange plasma are discussed, showing results such as the relationship between neutralizer emission current and plasma beam potential, ion energies as a function of neutralizer bias, charge-exchange ion current collected by an axially moving Faraday cup-RPA for 8-cm and 30-cm ion thrusters, beam density and potential data from a 15-cm ion thruster, and charge-exchange ion flow around a 30-cm thruster. A 20-cm thruster electrical configuration is depicted and facility effects are discussed. Finally, plasma modeling is covered in detail for plasma beam and charge-exchange plasma.

Beyond Poisson-Boltzmann: Fluctuation effects and correlation functions

NASA Astrophysics Data System (ADS)

Netz, R. R.; Orland, H.

2000-02-01

We formulate the exact non-linear field theory for a fluctuating counter-ion distribution in the presence of a fixed, arbitrary charge distribution. The Poisson-Boltzmann equation is obtained as the saddle-point of the field-theoretic action, and the effects of counter-ion fluctuations are included by a loop-wise expansion around this saddle point. The Poisson equation is obeyed at each order in this loop expansion. We explicitly give the expansion of the Gibbs potential up to two loops. We then apply our field-theoretic formalism to the case of a single impenetrable wall with counter ions only (in the absence of salt ions). We obtain the fluctuation corrections to the electrostatic potential and the counter-ion density to one-loop order without further approximations. The relative importance of fluctuation corrections is controlled by a single parameter, which is proportional to the cube of the counter-ion valency and to the surface charge density. The effective interactions and correlation functions between charged particles close to the charged wall are obtained on the one-loop level.

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

NASA Astrophysics Data System (ADS)

Ferri, Nicola; Ambrosetti, Alberto; Tkatchenko, Alexandre

2017-07-01

Electronic charge rearrangements at interfaces between organic molecules and solid surfaces play a key role in a wide range of applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. It is common to utilize electrostatics and Pauli pushback to control the interface electronic properties, while the ubiquitous van der Waals (vdW) interactions are often considered to have a negligible direct contribution (beyond the obvious structural relaxation). Here, we apply a fully self-consistent Tkatchenko-Scheffler vdW density functional to demonstrate that the weak vdW interactions can induce sizable charge rearrangements at hybrid metal/organic systems (HMOS). The complex vdW correlation potential smears out the interfacial electronic density, thereby reducing the charge transfer in HMOS, changes the interface work functions by up to 0.2 eV, and increases the interface dipole moment by up to 0.3 Debye. Our results suggest that vdW interactions should be considered as an additional control parameter in the design of hybrid interfaces with the desired electronic properties.

Counterintuitive electron localisation from density-functional theory with polarisable solvent models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dale, Stephen G., E-mail: sdale@ucmerced.edu; Johnson, Erin R., E-mail: erin.johnson@dal.ca

2015-11-14

Exploration of the solvated electron phenomena using density-functional theory (DFT) generally results in prediction of a localised electron within an induced solvent cavity. However, it is well known that DFT favours highly delocalised charges, rendering the localisation of a solvated electron unexpected. We explore the origins of this counterintuitive behaviour using a model Kevan-structure system. When a polarisable-continuum solvent model is included, it forces electron localisation by introducing a strong energetic bias that favours integer charges. This results in the formation of a large energetic barrier for charge-hopping and can cause the self-consistent field to become trapped in local minimamore » thus converging to stable solutions that are higher in energy than the ground electronic state. Finally, since the bias towards integer charges is caused by the polarisable continuum, these findings will also apply to other classical polarisation corrections, as in combined quantum mechanics and molecular mechanics (QM/MM) methods. The implications for systems beyond the solvated electron, including cationic DNA bases, are discussed.« less

A stochastic model for photon noise induced by charged particles in multiplier phototubes of the space telescope fine guidance sensors

NASA Technical Reports Server (NTRS)

Howell, L. W.; Kennel, H. F.

1984-01-01

The Space Telescope (ST) is subjected to charged particle strikes in its space environment. ST's onboard fine guidance sensors utilize multiplier phototubes (PMT) for attitude determination. These tubes, when subjected to charged particle strikes, generate spurious photons in the form of Cerenkov radiation and fluorescence which give rise to unwanted disturbances in the pointing of the telescope. A stochastic model for the number of these spurious photons which strike the photocathode of the multiplier phototube which in turn produce the unwanted photon noise are presented. The model is applicable to both galactic cosmic rays and charged particles trapped in the Earth's radiation belts. The model which was programmed allows for easy adaption to a wide range of particles and different parameters for the phototube of the multiplier. The probability density functions for photons noise caused by protons, alpha particles, and carbon nuclei were using thousands of simulated strikes. These distributions are used as part of an overall ST dynamics simulation. The sensitivity of the density function to changes in the window parameters was also investigated.

Stochastic model for photon noise induced by charged particles in multiplier phototubes of the Hubble Space Telescope fine guidance sensors

NASA Technical Reports Server (NTRS)

Howell, L. W.; Kennel, H. F.

1986-01-01

The Space Telescope (ST) is subjected to charged particle strikes in its space environment. ST's onboard fine guidance sensors utilize multiplier phototubes (PMT) for attitude determination. These tubes, when subjected to charged particle strikes, generate spurious photons in the form of Cerenkov radiation and fluorescence which give rise to unwanted disturbances in the pointing of the telescope. A stochastic model for the number of these spurious photons which strike the photocathodes of the multiplier phototube which in turn produce the unwanted photon noise are presented. The model is applicable to both galactic cosmic rays and charged particles trapped in the earth's radiation belts. The model which was programmed allows for easy adaption to a wide range of particles and different parameters for the phototube of the multiplier. The probability density functions for photons noise caused by protons, alpha particles, and carbon nuclei were using thousands of simulated strikes. These distributions are used as part of an overall ST dynamics simulation. The sensitivity of the density function to changes in the window parameters was also investigated.

Topology of charge density of flucytosine and related molecules and characteristics of their bond charge distributions.

PubMed

Murgich, Juan; Franco, Héctor J; San-Blas, Gioconda

2006-08-24

The molecular charge distribution of flucytosine (4-amino-5-fluoro-2-pyrimidone), uracil, 5-fluorouracil, and thymine was studied by means of density functional theory calculations (DFT). The resulting distributions were analyzed by means of the atoms in molecules (AIM) theory. Bonds were characterized through vectors formed with the charge density value, its Laplacian, and the bond ellipticity calculated at the bond critical point (BCP). Within each set of C=O, C-H, and N-H bonds, these vectors showed little dispersion. C-C bonds formed three different subsets, one with a significant degree of double bonding, a second corresponding to single bonds with a finite ellipticity produced by hyperconjugation, and a third one formed by a pure single bond. In N-C bonds, a decrease in bond length (an increase in double bond character) was not reflected as an increase in their ellipticity, as in all C-C bonds studied. It was also found that substitution influenced the N-C, C-O, and C-C bond ellipticity much more than density and its Laplacian at the BCP. The Laplacian of charge density pointed to the existence of both bonding and nonbonding maxima in the valence shell charge concentration of N, O, and F, while only bonding ones were found for the C atoms. The nonbonding maxima related to the sites for electrophilic attack and H bonding in O and N, while sites of nucleophilic attack were suggested by the holes in the valence shell of the C atoms of the carbonyl groups.

Adsorption and Dissociation of Molecular Oxygen on the (0001) Surface of Double Hexagonal Close Packed Americium

NASA Astrophysics Data System (ADS)

Dholabhai, Pratik; Atta-Fynn, Raymond; Ray, Asok

2008-03-01

Oxygen molecule adsorption on (0001) surface of double hexagonal packed americium has been studied in detail within the framework of density functional theory using a full-potential all-electron linearized augmented plane wave plus local orbitals method. The most stable configuration corresponded to molecular dissociation with the oxygen atoms occupying neighboring three-fold hollow h3 sites. Chemisorption energies and adsorption geometries for the adsorbed species, and change in work functions, magnetic moments, partial charges inside muffin-tins, difference charge density distributions and density of states for the bare Am slab and the Am slab after adsorption of the oxygen molecule will be discussed. The effects of chemisorption on Am 5f electron localization-delocalization in the vicinity of the Fermi level and the reaction barrier calculation for the dissociation of oxygen molecule to the most stable h3 sites will be discussed.

Electrical double layers and differential capacitance in molten salts from density functional theory

DOE PAGES

Frischknecht, Amalie L.; Halligan, Deaglan O.; Parks, Michael L.

2014-08-05

Classical density functional theory (DFT) is used to calculate the structure of the electrical double layer and the differential capacitance of model molten salts. The DFT is shown to give good qualitative agreement with Monte Carlo simulations in the molten salt regime. The DFT is then applied to three common molten salts, KCl, LiCl, and LiKCl, modeled as charged hard spheres near a planar charged surface. The DFT predicts strong layering of the ions near the surface, with the oscillatory density profiles extending to larger distances for larger electrostatic interactions resulting from either lower temperature or lower dielectric constant. Inmore » conclusion, overall the differential capacitance is found to be bell-shaped, in agreement with recent theories and simulations for ionic liquids and molten salts, but contrary to the results of the classical Gouy-Chapman theory.« less

Estimation of Nanodiamond Surface Charge Density from Zeta Potential and Molecular Dynamics Simulations.

PubMed

Ge, Zhenpeng; Wang, Yi

2017-04-20

Molecular dynamics simulations of nanoparticles (NPs) are increasingly used to study their interactions with various biological macromolecules. Such simulations generally require detailed knowledge of the surface composition of the NP under investigation. Even for some well-characterized nanoparticles, however, this knowledge is not always available. An example is nanodiamond, a nanoscale diamond particle with surface dominated by oxygen-containing functional groups. In this work, we explore using the harmonic restraint method developed by Venable et al., to estimate the surface charge density (σ) of nanodiamonds. Based on the Gouy-Chapman theory, we convert the experimentally determined zeta potential of a nanodiamond to an effective charge density (σ eff ), and then use the latter to estimate σ via molecular dynamics simulations. Through scanning a series of nanodiamond models, we show that the above method provides a straightforward protocol to determine the surface charge density of relatively large (> ∼100 nm) NPs. Overall, our results suggest that despite certain limitation, the above protocol can be readily employed to guide the model construction for MD simulations, which is particularly useful when only limited experimental information on the NP surface composition is available to a modeler.

Extended Lagrangian Density Functional Tight-Binding Molecular Dynamics for Molecules and Solids.

PubMed

Aradi, Bálint; Niklasson, Anders M N; Frauenheim, Thomas

2015-07-14

A computationally fast quantum mechanical molecular dynamics scheme using an extended Lagrangian density functional tight-binding formulation has been developed and implemented in the DFTB+ electronic structure program package for simulations of solids and molecular systems. The scheme combines the computational speed of self-consistent density functional tight-binding theory with the efficiency and long-term accuracy of extended Lagrangian Born-Oppenheimer molecular dynamics. For systems without self-consistent charge instabilities, only a single diagonalization or construction of the single-particle density matrix is required in each time step. The molecular dynamics simulation scheme can be applied to a broad range of problems in materials science, chemistry, and biology.

Dual descriptors within the framework of spin-polarized density functional theory.

PubMed

Chamorro, E; Pérez, P; Duque, M; De Proft, F; Geerlings, P

2008-08-14

Spin-polarized density functional theory (SP-DFT) allows both the analysis of charge-transfer (e.g., electrophilic and nucleophilic reactivity) and of spin-polarization processes (e.g., photophysical changes arising from electron transitions). In analogy with the dual descriptor introduced by Morell et al. [J. Phys. Chem. A 109, 205 (2005)], we introduce new dual descriptors intended to simultaneously give information of the molecular regions where the spin-polarization process linking states of different multiplicity will drive electron density and spin density changes. The electronic charge and spin rearrangement in the spin forbidden radiative transitions S(0)-->T(n,pi(*)) and S(0)-->T(pi,pi(*)) in formaldehyde and ethylene, respectively, have been used as benchmark examples illustrating the usefulness of the new spin-polarization dual descriptors. These quantities indicate those regions where spin-orbit coupling effects are at work in such processes. Additionally, the qualitative relationship between the topology of the spin-polarization dual descriptors and the vertical singlet triplet energy gap in simple substituted carbene series has been also discussed. It is shown that the electron density and spin density rearrangements arise in agreement with spectroscopic experimental evidence and other theoretical results on the selected target systems.

Density functional theory for d- and f-electron materials and compounds

DOE PAGES

Mattson, Ann E.; Wills, John M.

2016-02-12

Here, the fundamental requirements for a computationally tractable Density Functional Theory-based method for relativistic f- and (nonrelativistic) d-electron materials and compounds are presented. The need for basing the Kohn–Sham equations on the Dirac equation is discussed. The full Dirac scheme needs exchange-correlation functionals in terms of four-currents, but ordinary functionals, using charge density and spin-magnetization, can be used in an approximate Dirac treatment. The construction of a functional that includes the additional confinement physics needed for these materials is illustrated using the subsystem-functional scheme. If future studies show that a full Dirac, four-current based, exchange-correlation functional is needed, the subsystemmore » functional scheme is one of the few schemes that can still be used for constructing functional approximations.« less

Volume shift and charge instability of simple-metal clusters

NASA Astrophysics Data System (ADS)

Brajczewska, M.; Vieira, A.; Fiolhais, C.; Perdew, J. P.

1996-12-01

Experiment indicates that small clusters show changes (mostly contractions) of the bond lengths with respect to bulk values. We use the stabilized jellium model to study the self-expansion and self-compression of spherical clusters (neutral or ionized) of simple metals. Results from Kohn - Sham density functional theory are presented for small clusters of Al and Na, including negatively-charged ones. We also examine the stability of clusters with respect to charging.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Möller, Christian, E-mail: cmoeller@cismst.de; TU Ilmenau, Institut für Physik, Weimarer Str. 32, 98693 Ilmenau; Bartel, Til

Iron-boron (FeB) pairing is observed in the n-type region of a boron and phosphorus co-doped silicon sample which is unexpected from the FeB pair model of Kimerling and Benton. To explain the experimental data, the existing FeB pair model is extended by taking into account the electronic capture and emission rates at the interstitial iron (Fe{sub i}) trap level as a function of the charge carrier densities. According to this model, the charge state of the Fe{sub i} may be charged in n-type making FeB association possible. Further, FeB pair formation during illumination in p-type silicon is investigated. This permitsmore » the determination of the charge carrier density dependent FeB dissociation rate and in consequence allows to determine the acceptor concentration in the co-doped n-type silicon by lifetime measurement.« less

Constraints on rapidity-dependent initial conditions from charged-particle pseudorapidity densities and two-particle correlations

NASA Astrophysics Data System (ADS)

Ke, Weiyao; Moreland, J. Scott; Bernhard, Jonah E.; Bass, Steffen A.

2017-10-01

We study the initial three-dimensional spatial configuration of the quark-gluon plasma (QGP) produced in relativistic heavy-ion collisions using centrality and pseudorapidity-dependent measurements of the medium's charged particle density and two-particle correlations. A cumulant-generating function is first used to parametrize the rapidity dependence of local entropy deposition and extend arbitrary boost-invariant initial conditions to nonzero beam rapidities. The model is then compared to p +Pb and Pb + Pb charged-particle pseudorapidity densities and two-particle pseudorapidity correlations and systematically optimized using Bayesian parameter estimation to extract high-probability initial condition parameters. The optimized initial conditions are then compared to a number of experimental observables including the pseudorapidity-dependent anisotropic flows, event-plane decorrelations, and flow correlations. We find that the form of the initial local longitudinal entropy profile is well constrained by these experimental measurements.

Potassium-intercalated H2Pc films: Alkali-induced electronic and geometrical modifications

NASA Astrophysics Data System (ADS)

Nilson, K.; Åhlund, J.; Shariati, M.-N.; Schiessling, J.; Palmgren, P.; Brena, B.; Göthelid, E.; Hennies, F.; Huismans, Y.; Evangelista, F.; Rudolf, P.; Göthelid, M.; Mârtensson, N.; Puglia, C.

2012-07-01

X-ray spectroscopy studies of potassium intercalated metal-free phthalocyanine multilayers adsorbed on Al(110) have been undertaken. Photoelectron spectroscopy measurements show the presence of several charge states of the molecules upon K intercalation, due to a charge transfer from the alkali. In addition, the comparison of valence band photoemission spectra with the density functional theory calculations of the density of states of the H2Pc- anion indicates a filling of the formerly lowest unoccupied molecular orbital by charge transfer from the alkali. This is further confirmed by x-ray absorption spectroscopy (XAS) studies, which show a decreased density of unoccupied states. XAS measurements in different experimental geometries reveal that the molecules in the pristine film are standing upright on the surface or are only slightly tilted away from the surface normal but upon K intercalation, the molecular orientation is changed in that the tilt angle of the molecules increases.

Geometrical Description of fractional quantum Hall quasiparticles

NASA Astrophysics Data System (ADS)

Park, Yeje; Yang, Bo; Haldane, F. D. M.

2012-02-01

We examine a description of fractional quantum Hall quasiparticles and quasiholes suggested by a recent geometrical approach (F. D. M. Haldane, Phys. Rev. Lett. 108, 116801 (2011)) to FQH systems, where the local excess electric charge density in the incompressible state is given by a topologically-quantized ``guiding-center spin'' times the Gaussian curvature of a ``guiding-center metric tensor'' that characterizes the local shape of the correlation hole around electrons in the fluid. We use a phenomenological energy function with two ingredients: the shear distortion energy of area-preserving distortions of the fluid, and a local (short-range) approximation to the Coulomb energy of the fluctuation of charge density associated with the Gaussian curvature. Quasiparticles and quasiholes of the 1/3 Laughlin state are modeled as ``punctures'' in the incompressible fluid which then relax by geometric distortion which generates Gaussian curvature, giving rise to the charge-density profile around the topological excitation.

Evaluating the Sources of Graphene’s Resistivity Using Differential Conductance

DOE PAGES

Somphonsane, R.; Ramamoorthy, H.; He, G.; ...

2017-09-04

We explore the contributions to the electrical resistance of monolayer and bilayer graphene, revealing transitions between different regimes of charge carrier scattering. In monolayer graphene at low densities, a nonmonotonic variation of the resistance is observed as a function of temperature. Such behaviour is consistent with the influence of scattering from screened Coulomb impurities. At higher densities, the resistance instead varies in a manner consistent with the influence of scattering from acoustic and optical phonons. The crossover from phonon-, to charged-impurity, limited conduction occurs once the concentration of gate-induced carriers is reduced below that of the residual carriers. In bilayermore » graphene, the resistance exhibits a monotonic decrease with increasing temperature for all densities, with the importance of short-range impurity scattering resulting in a “universal” density-independent (scaled) conductivity at high densities. At lower densities, the conductivity deviates from this universal curve, pointing to the importance of thermal activation of carriers out of charge puddles. These various assignments, in both systems, are made possible by an approach of “differential-conductance mapping”, which allows us to suppress quantum corrections to reveal the underlying mechanisms governing the resistivity.« less

Evaluating the Sources of Graphene’s Resistivity Using Differential Conductance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Somphonsane, R.; Ramamoorthy, H.; He, G.

We explore the contributions to the electrical resistance of monolayer and bilayer graphene, revealing transitions between different regimes of charge carrier scattering. In monolayer graphene at low densities, a nonmonotonic variation of the resistance is observed as a function of temperature. Such behaviour is consistent with the influence of scattering from screened Coulomb impurities. At higher densities, the resistance instead varies in a manner consistent with the influence of scattering from acoustic and optical phonons. The crossover from phonon-, to charged-impurity, limited conduction occurs once the concentration of gate-induced carriers is reduced below that of the residual carriers. In bilayermore » graphene, the resistance exhibits a monotonic decrease with increasing temperature for all densities, with the importance of short-range impurity scattering resulting in a “universal” density-independent (scaled) conductivity at high densities. At lower densities, the conductivity deviates from this universal curve, pointing to the importance of thermal activation of carriers out of charge puddles. These various assignments, in both systems, are made possible by an approach of “differential-conductance mapping”, which allows us to suppress quantum corrections to reveal the underlying mechanisms governing the resistivity.« less

Constrained subsystem density functional theory.

PubMed

Ramos, Pablo; Pavanello, Michele

2016-08-03

Constrained Subsystem Density Functional Theory (CSDFT) allows to compute diabatic states for charge transfer reactions using the machinery of the constrained DFT method, and at the same time is able to embed such diabatic states in a molecular environment via a subsystem DFT scheme. The CSDFT acronym is chosen to reflect the fact that on top of the subsystem DFT approach, a constraining potential is applied to each subsystem. We show that CSDFT can successfully tackle systems as complex as single stranded DNA complete of its backbone, and generate diabatic states as exotic as a hole localized on a phosphate group as well as on the nucleobases. CSDFT will be useful to investigators needing to evaluate the environmental effect on charge transfer couplings for systems in condensed phase environments.

Bond Dissociation Energies of the Tungsten Fluorides and Their Singly-Charged Ions: A Density Functional Survey

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.; Arnold, James (Technical Monitor)

1999-01-01

The dissociation of WF6 and the related singly-charged cations and anions into the lower fluorides and fluorine atoms has been investigated theoretically using density functional theory (B3LYP) and relativistic effective core potentials, with estimates of spin-orbit effects included using a simple model. The inclusion of spin-orbit is essential for a correct description of the thermochemistry. The total atomization energy of the neutral and anionic WF6 is reproduced to within 25 kcal/mol, but comparison of individual bond dissociation energies with available experimental data shows discrepancies of up to 10 kcal/mol. The results are nevertheless useful to help resolve discrepancies in experimental data and provide estimates of missing data.

Local entanglement entropy of fermions as a marker of quantum phase transition in the one-dimensional Hubbard model

NASA Astrophysics Data System (ADS)

Cha, Min-Chul; Chung, Myung-Hoon

2018-05-01

We study quantum phase transition of interacting fermions by measuring the local entanglement entropy in the one-dimensional Hubbard model. The reduced density matrices for blocks of a few sites are constructed from the ground state wave function in infinite systems by adopting the matrix product state representation where time-evolving block decimations are performed to obtain the lowest energy states. The local entanglement entropy, constructed from the reduced density matrices, as a function of the chemical potential shows clear signatures of the Mott transition. The value of the central charge, numerically determined from the universal properties of the local entanglement entropy, confirms that the transition is caused by the suppression of the charge degrees of freedom.

Interconfigurational energies in transition-metal atoms using gradient-corrected density-functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kutzler, F.W.; Painter, G.S.

1991-03-15

The rapid variation of charge and spin densities in atoms and molecules provides a severe test for local-density-functional theory and for the use of gradient corrections. In the study reported in this paper, we use the Langreth, Mehl, and Hu (LMH) functional and the generalized gradient approximation (GGA) of Perdew and Yue to calculate {ital s}-{ital d} transition energies, 4{ital s} ionization energies, and 3{ital d} ionization energies for the 3{ital d} transition-metal atoms. These calculations are compared with results from the local-density functional of Vosko, Wilk, and Nusair. By comparison with experimental energies, we find that the gradient functionalsmore » are only marginally more successful than the local-density approximation in calculating energy differences between states in transition-metal atoms. The GGA approximation is somewhat better than the LMH functional for most of the atoms studied, although there are several exceptions.« less

Persistent Charge-Density-Wave Order in Single-Layer TaSe2.

PubMed

Ryu, Hyejin; Chen, Yi; Kim, Heejung; Tsai, Hsin-Zon; Tang, Shujie; Jiang, Juan; Liou, Franklin; Kahn, Salman; Jia, Caihong; Omrani, Arash A; Shim, Ji Hoon; Hussain, Zahid; Shen, Zhi-Xun; Kim, Kyoo; Min, Byung Il; Hwang, Choongyu; Crommie, Michael F; Mo, Sung-Kwan

2018-02-14

We present the electronic characterization of single-layer 1H-TaSe 2 grown by molecular beam epitaxy using a combined angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory calculations. We demonstrate that 3 × 3 charge-density-wave (CDW) order persists despite distinct changes in the low energy electronic structure highlighted by the reduction in the number of bands crossing the Fermi energy and the corresponding modification of Fermi surface topology. Enhanced spin-orbit coupling and lattice distortion in the single-layer play a crucial role in the formation of CDW order. Our findings provide a deeper understanding of the nature of CDW order in the two-dimensional limit.

The effect of plasma density and emitter geometry on space charge limits for field emitter array electron charge emission into a space plasma

NASA Astrophysics Data System (ADS)

Morris, Dave; Gilchrist, Brian; Gallimore, Alec

2001-02-01

Field Emitter Array Cathodes (FEACs) are a new technology being developed for several potential spacecraft electron emission and charge control applications. Instead of a single hot (i.e., high powered) emitter, or a gas dependant plasma contactor, FEAC systems consist of many (hundreds or thousands) of small (micron level) cathode/gate pairs printed on a semiconductor wafer that effect cold field emission at relatively low voltages. Each individual cathode emits only micro-amp level currents, but a functional array is capable of amp/cm2 current densities. It is hoped that thus FEAC offers the possibility of a relatively low-power, simple to integrate, and inexpensive technique for the high level of current emissions that are required for an electrodynamic tether (EDT) propulsion mission. Space charge limits are a significant concern for the EDT application. Vacuum chamber tests and PIC simulations are being performed at the University of Michigan Plasmadynamics and Electric Propulsion Laboratory and Space Physics Research Laboratory to determine the effect of plasma density and emitter geometry on space charge limitations. The results of this work and conclusions to date of how to best mitigate space charge limits will be presented. .

Investigation of surface charge density on solid-liquid interfaces by modulating the electrical double layer.

PubMed

Moon, Jong Kyun; Song, Myung Won; Pak, Hyuk Kyu

2015-05-20

A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid-liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid-liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a dc bias voltage across the plates, an ac electric current can be generated. By measuring the voltage drop across a load resistor as a function of bias voltage, we can study the surface charge density on solid-liquid interfaces. Our experimental results agree very well with the simple equivalent electrical circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. We expect this method to aid in the study of electrical phenomena on solid-liquid interfaces.

Derivation of Poisson and Nernst-Planck equations in a bath and channel from a molecular model.

PubMed

Schuss, Z; Nadler, B; Eisenberg, R S

2001-09-01

Permeation of ions from one electrolytic solution to another, through a protein channel, is a biological process of considerable importance. Permeation occurs on a time scale of micro- to milliseconds, far longer than the femtosecond time scales of atomic motion. Direct simulations of atomic dynamics are not yet possible for such long-time scales; thus, averaging is unavoidable. The question is what and how to average. In this paper, we average a Langevin model of ionic motion in a bulk solution and protein channel. The main result is a coupled system of averaged Poisson and Nernst-Planck equations (CPNP) involving conditional and unconditional charge densities and conditional potentials. The resulting NP equations contain the averaged force on a single ion, which is the sum of two components. The first component is the gradient of a conditional electric potential that is the solution of Poisson's equation with conditional and permanent charge densities and boundary conditions of the applied voltage. The second component is the self-induced force on an ion due to surface charges induced only by that ion at dielectric interfaces. The ion induces surface polarization charge that exerts a significant force on the ion itself, not present in earlier PNP equations. The proposed CPNP system is not complete, however, because the electric potential satisfies Poisson's equation with conditional charge densities, conditioned on the location of an ion, while the NP equations contain unconditional densities. The conditional densities are closely related to the well-studied pair-correlation functions of equilibrium statistical mechanics. We examine a specific closure relation, which on the one hand replaces the conditional charge densities by the unconditional ones in the Poisson equation, and on the other hand replaces the self-induced force in the NP equation by an effective self-induced force. This effective self-induced force is nearly zero in the baths but is approximately equal to the self-induced force in and near the channel. The charge densities in the NP equations are interpreted as time averages over long times of the motion of a quasiparticle that diffuses with the same diffusion coefficient as that of a real ion, but is driven by the averaged force. In this way, continuum equations with averaged charge densities and mean-fields can be used to describe permeation through a protein channel.

Chemical bonding analysis on amphoteric hydrogen - alkaline earth ammine borohydrides

NASA Astrophysics Data System (ADS)

Kiruthika, S.; Ravindran, P.

2018-04-01

Usually the ions in solid are in the positive oxidation states or in the negative oxidation state depending upon the chemical environment. It is highly unusual for an ion having both positive as well as negative oxidation state in a particular compound. Structural analysis suggest that the alkaline earth ammine borohydrides (AABH) with the chemical formula M (BH4)2(NH3)2 (M = Mg, Ca, or Sr) where hydrogen is present in +1 and -1 oxidation states. In order to understand the oxidation states of hydrogen and also the character of chemical bond present in AABH we have made charge density, electron localization function, Born effective charge, Bader effective charge, and density of states analyses using result from the density functional calculations. Our detailed analyses show that hydrogen is in amphoteric behavior with hydrogen closer to boron is in negative oxidation state and that closer to nitrogen is in the positive oxidation state. Due to the presence of finite covalent bonding between the consitutents in AABH the oxidation state of hydrogen is non-interger value. The confirmation of the presence of amphtoric behavior of hydrogen in AABH has implication in hydrogen storage applications.

Log-rise of the resistivity in the holographic Kondo model

NASA Astrophysics Data System (ADS)

Padhi, Bikash; Tiwari, Apoorv; Setty, Chandan; Phillips, Philip W.

2018-03-01

We study a single-channel Kondo effect using a recently developed [1-4] holographic large-N technique. In order to obtain resistivity of this model, we introduce a probe field. The gravity dual of a localized fermionic impurity in 1 +1 -dimensional host matter is constructed by embedding a localized two-dimensional Anti-de Sitter (AdS2 )-brane in the bulk of three-dimensional AdS3 . This helps us construct an impurity charge density which acts as a source to the bulk equation of motion of the probe gauge field. The functional form of the charge density is obtained independently by solving the equations of motion for the fields confined to the AdS2 -brane. The asymptotic solution of the probe field is dictated by the impurity charge density, which in turn affects the current-current correlation functions and hence the resistivity. Our choice of parameters tunes the near-boundary impurity current to be marginal, resulting in a log T behavior in the UV resistivity, as is expected for the Kondo problem. The resistivity at the IR fixed point turns out to be zero, signaling a complete screening of the impurity.

Microscopic origin of the charge transfer in single crystals based on thiophene derivatives: A combined NEXAFS and density functional theory approach

NASA Astrophysics Data System (ADS)

Chernenkaya, A.; Morherr, A.; Backes, S.; Popp, W.; Witt, S.; Kozina, X.; Nepijko, S. A.; Bolte, M.; Medjanik, K.; Öhrwall, G.; Krellner, C.; Baumgarten, M.; Elmers, H. J.; Schönhense, G.; Jeschke, H. O.; Valentí, R.

2016-07-01

We have investigated the charge transfer mechanism in single crystals of DTBDT-TCNQ and DTBDT-F4TCNQ (where DTBDT is dithieno[2,3-d;2',3'-d'] benzo[1,2-b;4,5-b']dithiophene) using a combination of near-edge X-ray absorption spectroscopy (NEXAFS) and density functional theory calculations (DFT) including final state effects beyond the sudden state approximation. In particular, we find that a description that considers the partial screening of the electron-hole Coulomb correlation on a static level as well as the rearrangement of electronic density shows excellent agreement with experiment and allows to uncover the details of the charge transfer mechanism in DTBDT-TCNQ and DTBDT-F4 TCNQ, as well as a reinterpretation of previous NEXAFS data on pure TCNQ. Finally, we further show that almost the same quality of agreement between theoretical results and experiment is obtained by the much faster Z+1/2 approximation, where the core hole effects are simulated by replacing N or F with atomic number Z with the neighboring atom with atomic number Z+1/2.

Quantum mechanical study and spectroscopic (FT-IR, FT-Raman, 13C, 1H) study, first order hyperpolarizability, NBO analysis, HOMO and LUMO analysis of 2-acetoxybenzoic acid by density functional methods

NASA Astrophysics Data System (ADS)

Bhavani, K.; Renuga, S.; Muthu, S.; Sankara narayanan, K.

2015-02-01

In this work, colorless crystals of 2-acetoxybenzoic acid were grown by slow evaporation method and the FT-IR and FT-Raman spectra of the sample were recorded in the region 4000-500 cm-1 and 4000-100 cm-1 respectively. Molecular structure is optimized with the help of density functional theory method (B3LYP) with 6-31+G(d,p), 6-311++G(d,p) basis sets. Stability of the molecule arising from hyperconjugation and charge delocalization is confirmed by the natural bond orbital analysis (NBO). The results show that electron density (ED) in the σ∗ antibonding orbitals and E(2) energies confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis following the scaled quantum mechanical force field (SQMFF) methodology. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO method. Mulliken population analysis on atomic charges is also calculated. The calculated HOMO and LUMO energy gap shows that charge transfer occurs within the molecule.

On the exchange-hole model of London dispersion forces

NASA Astrophysics Data System (ADS)

Ángyán, János G.

2007-07-01

First-principles derivation is given for the heuristic exchange-hole model of London dispersion forces by Becke and Johnson [J. Chem. Phys. 122, 154104 (2005)]. A one-term approximation is used for the dynamic charge density response function, and it is shown that a central nonempirical ingredient of the approximate nonexpanded dispersion energy is the charge density autocorrelation function, a two-particle property, related to the exchange-correlation hole. In the framework of a dipolar approximation of the Coulomb interaction around the molecular origin, one obtains the so-called Salem-Tang-Karplus approximation to the C6 dispersion coefficient. Alternatively, by expanding the Coulomb interaction around the center of charge (centroid) of the exchange-correlation hole associated with each point in the molecular volume, a multicenter expansion is obtained around the centroids of electron localization domains, always in terms of the exchange-correlation hole. In order to get a formula analogous to that of Becke and Johnson, which involves the exchange-hole only, further assumptions are needed, related to the difficulties of obtaining the expectation value of a two-electron operator from a single determinant. Thus a connection could be established between the conventional fluctuating charge density model of London dispersion forces and the notion of the "exchange-hole dipole moment" shedding some light on the true nature of the approximations implicit in the Becke-Johnson model.

Entropic effects in the electric double layer of model colloids with size-asymmetric monovalent ions

NASA Astrophysics Data System (ADS)

Guerrero-García, Guillermo Iván; González-Tovar, Enrique; Olvera de la Cruz, Mónica

2011-08-01

The structure of the electric double layer of charged nanoparticles and colloids in monovalent salts is crucial to determine their thermodynamics, solubility, and polyion adsorption. In this work, we explore the double layer structure and the possibility of charge reversal in relation to the size of both counterions and coions. We examine systems with various size-ratios between counterions and coions (ion size asymmetries) as well as different total ion volume fractions. Using Monte Carlo simulations and integral equations of a primitive-model electric double layer, we determine the highest charge neutralization and electrostatic screening near the electrified surface. Specifically, for two binary monovalent electrolytes with the same counterion properties but differing only in the coion's size surrounding a charged nanoparticle, the one with largest coion size is found to have the largest charge neutralization and screening. That is, in size-asymmetric double layers with a given counterion's size the excluded volume of the coions dictates the adsorption of the ionic charge close to the colloidal surface for monovalent salts. Furthermore, we demonstrate that charge reversal can occur at low surface charge densities, given a large enough total ion concentration, for systems of monovalent salts in a wide range of ion size asymmetries. In addition, we find a non-monotonic behavior for the corresponding maximum charge reversal, as a function of the colloidal bare charge. We also find that the reversal effect disappears for binary salts with large-size counterions and small-size coions at high surface charge densities. Lastly, we observe a good agreement between results from both Monte Carlo simulations and the integral equation theory across different colloidal charge densities and 1:1-elec-trolytes with different ion sizes.

Magnetic field effects on charge structure factors of gapped graphene structure

NASA Astrophysics Data System (ADS)

Rezania, Hamed; Tawoose, Nasrin

2018-02-01

We present the behaviors of dynamical and static charge susceptibilities of undoped gapped graphene using the Green's function approach in the context of tight binding model Hamiltonian. Specially, the effects of magnetic field on the plasmon modes of gapped graphene structure are investigated via calculating correlation function of charge density operators. Our results show the increase of magnetic field leads to disappear high frequency plasmon mode for gapped case. We also show that low frequency plasmon mode has not affected by increase of magnetic field and chemical potential. Finally the temperature dependence of static charge structure factor of gapp graphene structure is studied. The effects of both magnetic field and gap parameter on the static structure factor are discusses in details.

On the work function and the charging of small ( r ≤ 5 nm) nanoparticles in plasmas

NASA Astrophysics Data System (ADS)

Kalered, E.; Brenning, N.; Pilch, I.; Caillault, L.; Minéa, T.; Ojamäe, L.

2017-01-01

The growth of nanoparticles (NPs) in plasmas is an attractive technique where improved theoretical understanding is needed for quantitative modeling. The variation of the work function W with size for small NPs, rN P≤ 5 nm, is a key quantity for modeling of three NP charging processes that become increasingly important at a smaller size: electron field emission, thermionic electron emission, and electron impact detachment. Here we report the theoretical values of the work function in this size range. Density functional theory is used to calculate the work functions for a set of NP charge numbers, sizes, and shapes, using copper for a case study. An analytical approximation is shown to give quite accurate work functions provided that rN P > 0.4 nm, i.e., consisting of about >20 atoms, and provided also that the NPs have relaxed close to spherical shape. For smaller sizes, W deviates from the approximation, and also depends on the charge number. Some consequences of these results for nanoparticle charging are outlined. In particular, a decrease in W for NP radius below about 1 nm has fundamental consequences for their charge in a plasma environment, and thereby on the important processes of NP nucleation, early growth, and agglomeration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sim, Eunji; Kim, Min-Cheol; Burke, Kieron

We investigate dissociation of diatomic molecules using standard density functional theory (DFT) and density-corrected density functional theory (DC-DFT) compared with CCSD(T) results as reference. The results show the difference between the HOMO values of dissociated atomic species often can be used as an indicator whether DFT would predict the correct dissociation limit. DFT predicts incorrect dissociation limits and charge distribution in molecules or molecular ions when the fragments have large HOMO differences, while DC-DFT and CCSD(T) do not. The criteria for large HOMO difference is about 2 ∼ 4 eV.

Molecular orbital studies (hardness, chemical potential, electronegativity and electrophilicity), vibrational spectroscopic investigation and normal coordinate analysis of 5-{1-hydroxy-2-[(propan-2-yl)amino]ethyl}benzene-1,3-diol

NASA Astrophysics Data System (ADS)

Muthu, S.; Renuga, S.

2014-01-01

FT-IR and FT-Raman spectra of 5-{1-hydroxy-2-[(propan-2-yl) amino] ethyl} benzene-1,3-diol (abbrevi- 54 ated as HPAEBD) were recorded in the region 4000-450 cm-1 and 4000-100 cm-1 respectively. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (B3LYP) and HF method with 6-31 G(d,p) as basis set. The theoretical wave numbers were scaled and compared with experimental FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated Potential energy distribution (PED). Stability of the molecule arising from hyperconjugation and charge delocalization is confirmed by the natural bond orbital analysis (NBO). The results show that electron density (ED) in the σ antibonding orbitals and E (2) energies confirm the occurrence of intra molecular charge transfer (ICT) within the molecule. The molecule orbital contributions were studied by using the total (TDOS), sum of α and β electron (αβDOS) density of States. Mulliken population analysis of atomic charges is also calculated. The calculated HOMO and LUMO energy gap shows that charge transfer occurs within the molecule. The electron density-based local reactivity descriptors such as Fukui functions were calculated to explain the chemical selectivity or reactivity site in this compound. On the basis of vibrational analyses, the thermodynamic properties of title compound at different temperatures have been calculated.

Density functional theory and molecular dynamics study of the uranyl ion (UO₂)²⁺.

PubMed

Rodríguez-Jeangros, Nicolás; Seminario, Jorge M

2014-03-01

The detection of uranium is very important, especially in water and, more importantly, in the form of uranyl ion (UO₂)²⁺, which is one of its most abundant moieties. Here, we report analyses and simulations of uranyl in water using ab initio modified force fields for water with improved parameters and charges of uranyl. We use a TIP4P model, which allows us to obtain accurate water properties such as the boiling point and the second and third shells of water molecules in the radial distribution function thanks to a fictitious charge that corrects the 3-point models by reproducing the exact dipole moment of the water molecule. We also introduced non-bonded interaction parameters for the water-uranyl intermolecular force field. Special care was taken in testing the effect of a range of uranyl charges on the structure of uranyl-water complexes. Atomic charges of the solvated ion in water were obtained using density functional theory (DFT) calculations taking into account the presence of nitrate ions in the solution, forming a neutral ensemble. DFT-based force fields were calculated in such a way that water properties, such as the boiling point or the pair distribution function stand. Finally, molecular dynamics simulations of a water box containing uranyl cations and nitrate anions are performed at room temperature. The three peaks in the oxygen-oxygen radial distribution function for water were found to be kept in the presence of uranyl thanks to the improvement of interaction parameters and charges. Also, we found three shells of water molecules surrounding the uranyl ion instead of two as was previously thought.

Hybrid density functional study on the mechanism for the enhanced photocatalytic properties of the ultrathin hybrid layered nanocomposite g-C3N4/BiOCl

NASA Astrophysics Data System (ADS)

Yao, Wenzhi; Zhang, Jihua; Wang, Yuanxu; Ren, Fengzhu

2018-03-01

To investigate the origin of the high photocatalytic performance of experimentally synthesized g-C3N4/ BiOCl, we studied its geometry structure, electronic structure, and photocatalytic properties by means of hybrid density-functional theory (DFT). The calculated band alignment of g-C3N4 and few-layer BiOCl sheets clearly shows that g-C3N4/ BiOCl is a standard type-II nanocomposite. The density of states, Bader charge, partial charge density, charge density difference, and the effective masses show that electron-hole pair can be effectively separated in the g-C3N4/BiOCl interface. The calculated absorption coefficients indicate an obvious redshift of the absorption edge. The band gap of g-C3N4/BiOCl can be modulated by external electric field, and a semiconductor-semimetal transition is observed. The type-II vdW heterostructure is still maintained during the changes of external electric field. Especially, when the electric field reaches to +0.7 V/Å, the impurity states have been eliminated with the band gap of 2.3 eV. An analysis of optical properties shows that the absorption coefficient in the visible-light region is enhanced considerably as the electric-field strength increases. Our calculation results suggest that the ultrathin hybrid layered g-C3N4/BiOCl nanocomposite may have significant advantages for visible-light photocatalysis.

Development and application of a 2-electron reduced density matrix approach to electron transport via molecular junctions

NASA Astrophysics Data System (ADS)

Hoy, Erik P.; Mazziotti, David A.; Seideman, Tamar

2017-11-01

Can an electronic device be constructed using only a single molecule? Since this question was first asked by Aviram and Ratner in the 1970s [Chem. Phys. Lett. 29, 277 (1974)], the field of molecular electronics has exploded with significant experimental advancements in the understanding of the charge transport properties of single molecule devices. Efforts to explain the results of these experiments and identify promising new candidate molecules for molecular devices have led to the development of numerous new theoretical methods including the current standard theoretical approach for studying single molecule charge transport, i.e., the non-equilibrium Green's function formalism (NEGF). By pairing this formalism with density functional theory (DFT), a wide variety of transport problems in molecular junctions have been successfully treated. For some systems though, the conductance and current-voltage curves predicted by common DFT functionals can be several orders of magnitude above experimental results. In addition, since density functional theory relies on approximations to the exact exchange-correlation functional, the predicted transport properties can show significant variation depending on the functional chosen. As a first step to addressing this issue, the authors have replaced density functional theory in the NEGF formalism with a 2-electron reduced density matrix (2-RDM) method, creating a new approach known as the NEGF-RDM method. 2-RDM methods provide a more accurate description of electron correlation compared to density functional theory, and they have lower computational scaling compared to wavefunction based methods of similar accuracy. Additionally, 2-RDM methods are capable of capturing static electron correlation which is untreatable by existing NEGF-DFT methods. When studying dithiol alkane chains and dithiol benzene in model junctions, the authors found that the NEGF-RDM predicts conductances and currents that are 1-2 orders of magnitude below those of B3LYP and M06 DFT functionals. This suggests that the NEGF-RDM method could be a viable alternative to NEGF-DFT for molecular junction calculations.

Stability of multiply charged fullerene anions and cations

NASA Astrophysics Data System (ADS)

Wang, Yang; Zettergren, Henning; Alcamí, Manuel; Martín, Fernando

2009-09-01

We present a systematic study of the stability of highly charged cationic and anionic fullerenes whose most stable neutral counterparts follow the isolated pentagon rule (IPR). In agreement with recent studies, we have found that, for many highly charged fullerenes, non-IPR isomers are significantly more stable than the IPR ones. To understand this behavior, we compare the results of elaborate density-functional theory (DFT) calculations to those of a simple Hückel molecular-orbital theory in which the DFT energies of the corresponding neutral systems are used as a reference. The model leads to a reasonable estimate of the relative stability of the IPR and non-IPR isomers as a function of charge, which can be used to identify, among the thousands of possible isomers and charge states, the non-IPR species that are likely more stable than the IPR isomers.

Survival of charged ρ condensation at high temperature and density

NASA Astrophysics Data System (ADS)

Liu, Hao; Yu, Lang; Huang, Mei

2016-02-01

The charged vector ρ mesons in the presence of external magnetic fields at finite temperature T and chemical potential μ have been investigated in the framework of the Nambu-Jona-Lasinio model. We compute the masses of charged ρ mesons numerically as a function of the magnetic field for different values of temperature and chemical potential. The self-energy of the ρ meson contains the quark-loop contribution, i.e. the leading order contribution in 1/Nc expansion. The charged ρ meson mass decreases with the magnetic field and drops to zero at a critical magnetic field eBc, which indicates that the charged vector meson condensation, i.e. the electromagnetic superconductor can be induced above the critical magnetic field. Surprisingly, it is found that the charged ρ condensation can even survive at high temperature and density. At zero temperature, the critical magnetic field just increases slightly with the chemical potential, which indicates that charged ρ condensation might occur inside compact stars. At zero density, in the temperature range 0.2-0.5 GeV, the critical magnetic field for charged ρ condensation is in the range of 0.2-0.6 GeV2, which indicates that a high temperature electromagnetic superconductor might be created at LHC. Supported by the NSFC (11275213, 11261130311) (CRC 110 by DFG and NSFC), CAS Key Project (KJCX2-EW-N01), and Youth Innovation Promotion Association of CAS. L.Yu is Partially Supported by China Postdoctoral Science Foundation (2014M550841)

Vibrational spectra, NLO analysis, and HOMO-LUMO studies of 2-chloro-6-fluorobenzoic acid and 3,4-dichlorobenzoic acid by density functional method

NASA Astrophysics Data System (ADS)

Senthil kumar, J.; Arivazhagan, M.; Thangaraju, P.

2015-08-01

The FTIR and FT-Raman spectra of 2-chloro-6-fluorobenzoic acid and 3,4-dichlorobenzoic acid have been recorded in the region 4000-400 cm-1 and 3500-50 cm-1, respectively. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of fundamental modes of the compounds were carried out. The optimized molecular geometries, vibrational frequencies, thermodynamic properties and atomic charge of the compounds were calculated by using density functional theory (B3LYP) method with 6-311+G and 6-311++G basis sets. The difference between the observed and scaled wave number values of most of fundamentals is very small. Unambiguous vibration assignment of all the fundamentals is made up the total energy distribution (TED). The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules. Besides, molecular electro static potential (MESP), Mulliken's charge analysis, first order hyper polarizability and several thermodynamic properties were performed by the DFT method.

Covalent Co–O–V and Sb–N Bonds Enable Polyoxovanadate Charge Control

PubMed Central

2017-01-01

The formation of [{CoII(teta)2}{CoII2(tren)(teta)2}VIV15SbIII6O42(H2O)]·ca.9H2O [teta = triethylenetetraamine; tren = tris(2-aminoethyl)amine] illustrates a strategy toward reducing the molecular charge of polyoxovanadates, a key challenge in their use as components in single-molecule electronics. Here, a V–O–Co bond to a binuclear Co2+-centered complex and a Sb–N bond to the terminal N atom of a teta ligand of a mononuclear Co2+ complex allow for full charge compensation of the archetypal molecular magnet [V15Sb6O42(H2O)]6–. Density functional theory based electron localization function analysis demonstrates that the Sb–N bond has an electron density similar to that of a Sb–O bond. Magnetic exchange coupling between the VIV and CoII spin centers mediated via the Sb–N bridge is comparably weakly antiferromagnetic. PMID:28541697

Effect of Siloxane Ring Strain and Cation Charge Density on the Formation of Coordinately Unsaturated Metal Sites on Silica: Insights from Density Functional Theory (DFT) Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Ujjal; Zhang, Guanghui; Hu, Bo

2015-10-28

Amorphous silica (SiO 2) is commonly used as a support in heterogeneous catalysis. However, due to the structural disorder and temperature induced change of surface morphology, the structures of silica supported metal catalysts are difficult to determine. Most studies are primarily focused on understanding the interactions of different types of surface hydroxyl groups with metal ions. In comparison, the effect of siloxane ring size on the structure of silica supported metal catalysts and how it affects catalytic activity is poorly understood. Here, we have used density functional theory calculations to understand the effect of siloxane ring strain on structure andmore » activity of different monomeric Lewis acid metal sites on silica. In particular, we have found that large siloxane rings favor strong dative bonding interaction between metal ion and surface hydroxyls, leading to the formation of high-coordinate metal sites. In comparison, metal-silanol interaction is weak in small siloxane rings, resulting in low-coordinate metal sites. The physical origin of this size dependence is associated with siloxane ring strain, and, a correlation between metal-silanol interaction energy and ring strain energy has been observed. In addition to ring strain, the strength of the metal-silanol interaction also depends on the positive charge density of the cations. In fact, a correlation also exists between metal-silanol interaction energy and charge density of several first-row transition and post-transition metals. The theoretical results are compared with the EXAFS data of monomeric Zn(II) and Ga(III) ions grafted on silica. In conclusion, the molecular level insights of how metal ion coordination on silica depends on siloxane ring strain and cation charge density will be useful in the synthesis of new catalysts.« less

Apparent violation of the sum rule for exchange-correlation charges by generalized gradient approximations.

PubMed

Kohut, Sviataslau V; Staroverov, Viktor N

2013-10-28

The exchange-correlation potential of Kohn-Sham density-functional theory, vXC(r), can be thought of as an electrostatic potential produced by the static charge distribution qXC(r) = -(1∕4π)∇(2)vXC(r). The total exchange-correlation charge, QXC = ∫qXC(r) dr, determines the rate of the asymptotic decay of vXC(r). If QXC ≠ 0, the potential falls off as QXC∕r; if QXC = 0, the decay is faster than coulombic. According to this rule, exchange-correlation potentials derived from standard generalized gradient approximations (GGAs) should have QXC = 0, but accurate numerical calculations give QXC ≠ 0. We resolve this paradox by showing that the charge density qXC(r) associated with every GGA consists of two types of contributions: a continuous distribution and point charges arising from the singularities of vXC(r) at each nucleus. Numerical integration of qXC(r) accounts for the continuous charge but misses the point charges. When the point-charge contributions are included, one obtains the correct QXC value. These findings provide an important caveat for attempts to devise asymptotically correct Kohn-Sham potentials by modeling the distribution qXC(r).

Density functional theory calculations on transition metal atoms adsorbed on graphene monolayers

NASA Astrophysics Data System (ADS)

Dimakis, Nicholas; Flor, Fernando Antonio; Salgado, Andres; Adjibi, Kolade; Vargas, Sarah; Saenz, Justin

2017-11-01

Transition metal atom adsorption on graphene monolayers has been elucidated using periodic density functional theory under hybrid and generalized gradient approximation functionals. More specifically, we examined the adsorption of Cu, Fe, Zn, Ru, and Os on graphene monolayers by calculating, among others, the electronic density-of-states spectra of the adatom-graphene system and the overlap populations of the adatom with the nearest adsorbing graphene carbon atoms. These calculations reveal that Cu form primarily covalent bonds with graphene atoms via strong hybridization between the adatom orbitals and the sp band of the graphene substrate, whereas the interaction of the Ru and Os with graphene also contain ionic parts. Although the interaction of Fe with graphene atoms is mostly covalent, some charge transfer to graphene is also observed. The interaction of Zn with graphene is weak. Mulliken population analysis and charge contour maps are used to elucidate charge transfers between the adatom and the substrate. The adsorption strength is correlated with the metal adsorption energy and the height of the metal adatom from the graphene plane for the geometrically optimized adatom-graphene system. Our analysis shows that show that metal adsorption strength follows the adatom trend Ru ≈ Os > Fe > Cu > Zn, as verified by corresponding changes in the adsorption energies. The increased metal-carbon orbital overlap for the Ru relative to Os adatom is attributed to hybridization defects.

A quantum mechanical-Poisson-Boltzmann equation approach for studying charge flow between ions and a dielectric continuum

NASA Astrophysics Data System (ADS)

Gogonea, Valentin; Merz, Kenneth M.

2000-02-01

This paper presents a theoretical model for the investigation of charge transfer between ions and a solvent treated as a dielectric continuum media. The method is a combination of a semiempirical effective Hamiltonian with a modified Poisson-Boltzmann equation which includes charge transfer in the form of a surface charge density positioned at the dielectric interface. The new Poisson-Boltzmann equation together with new boundary conditions results in a new set of equations for the electrostatic potential (or polarization charge densities). Charge transfer adds a new free energy component to the solvation free energy term, which accounts for all interactions between the transferred charge at the dielectric interface, the solute wave function and the solvent polarization charges. Practical calculations on a set of 19 anions and 17 cations demonstrate that charge exchange with a dielectric is present and it is in the range of 0.06-0.4 eu. Furthermore, the pattern of the magnitudes of charge transfer can be related to the acid-base properties of the ions in many cases, but exceptions are also found. Finally, we show that the method leads to an energy decomposition scheme of the total electrostatic energy, which can be used in mechanistic studies on protein and DNA interaction with water.

Ion transport controlled by nanoparticle-functionalized membranes.

PubMed

Barry, Edward; McBride, Sean P; Jaeger, Heinrich M; Lin, Xiao-Min

2014-12-17

From proton exchange membranes in fuel cells to ion channels in biological membranes, the well-specified control of ionic interactions in confined geometries profoundly influences the transport and selectivity of porous materials. Here we outline a versatile new approach to control a membrane's electrostatic interactions with ions by depositing ligand-coated nanoparticles around the pore entrances. Leveraging the flexibility and control by which ligated nanoparticles can be synthesized, we demonstrate how ligand terminal groups such as methyl, carboxyl and amine can be used to tune the membrane charge density and control ion transport. Further functionality, exploiting the ligands as binding sites, is demonstrated for sulfonate groups resulting in an enhancement of the membrane charge density. We then extend these results to smaller dimensions by systematically varying the underlying pore diameter. As a whole, these results outline a previously unexplored method for the nanoparticle functionalization of membranes using ligated nanoparticles to control ion transport.

Ion transport controlled by nanoparticle-functionalized membranes

NASA Astrophysics Data System (ADS)

Barry, Edward; McBride, Sean P.; Jaeger, Heinrich M.; Lin, Xiao-Min

2014-12-01

From proton exchange membranes in fuel cells to ion channels in biological membranes, the well-specified control of ionic interactions in confined geometries profoundly influences the transport and selectivity of porous materials. Here we outline a versatile new approach to control a membrane’s electrostatic interactions with ions by depositing ligand-coated nanoparticles around the pore entrances. Leveraging the flexibility and control by which ligated nanoparticles can be synthesized, we demonstrate how ligand terminal groups such as methyl, carboxyl and amine can be used to tune the membrane charge density and control ion transport. Further functionality, exploiting the ligands as binding sites, is demonstrated for sulfonate groups resulting in an enhancement of the membrane charge density. We then extend these results to smaller dimensions by systematically varying the underlying pore diameter. As a whole, these results outline a previously unexplored method for the nanoparticle functionalization of membranes using ligated nanoparticles to control ion transport.

Theory of charge density wave depinning by electromechanical effect

NASA Astrophysics Data System (ADS)

Quémerais, P.

2017-03-01

We discuss the first theory for the depinning of low-dimensional, incommensurate, charge density waves (CDWs) in the strong electron-phonon (e-p) regime. Arguing that most real CDWs systems invariably develop a gigantic dielectric constant (GDC) at very low frequencies, we propose an electromechanical mechanism which is based on a local field effect. At zero electric field and large enough e-p coupling the structures are naturally pinned by the lattice due to its discreteness, and develop modulation functions which are characterized by discontinuities. When the electric field is turned on, we show that it exists a finite threshold value for the electric field above which the discontinuities of the modulation functions vanish due to CDW deformation. The CDW is then free to move. The signature of this pinning/depinning transition as a function of the increasing electric field can be directly observed in the phonon spectrum by using inelastic neutrons or X-rays experiments.

Energy decomposition analysis of single bonds within Kohn-Sham density functional theory.

PubMed

Levine, Daniel S; Head-Gordon, Martin

2017-11-28

An energy decomposition analysis (EDA) for single chemical bonds is presented within the framework of Kohn-Sham density functional theory based on spin projection equations that are exact within wave function theory. Chemical bond energies can then be understood in terms of stabilization caused by spin-coupling augmented by dispersion, polarization, and charge transfer in competition with destabilizing Pauli repulsions. The EDA reveals distinguishing features of chemical bonds ranging across nonpolar, polar, ionic, and charge-shift bonds. The effect of electron correlation is assessed by comparison with Hartree-Fock results. Substituent effects are illustrated by comparing the C-C bond in ethane against that in bis(diamantane), and dispersion stabilization in the latter is quantified. Finally, three metal-metal bonds in experimentally characterized compounds are examined: a [Formula: see text]-[Formula: see text] dimer, the [Formula: see text]-[Formula: see text] bond in dizincocene, and the Mn-Mn bond in dimanganese decacarbonyl.

High-energy Electron Scattering and the Charge Distributions of Selected Nuclei

DOE R&D Accomplishments Database

Hahn, B.; Ravenhall, D. G.; Hofstadter, R.

1955-10-01

Experimental results are presented of electron scattering by Ca, V, Co, In, Sb, Hf, Ta, W, Au, Bi, Th, and U, at 183 Mev and (for some of the elements) at 153 Mev. For those nuclei for which asphericity and inelastic scattering are absent or unimportant, i.e., Ca, V, Co, In, Sb, Au, and Bi, a partial wave analysis of the Dirac equation has been performed in which the nuclei are represented by static, spherically symmetric charge distributions. Smoothed uniform charge distributions have been assumed; these are characterized by a constant charge density in the central region of the nucleus, with a smoothed-our surface. Essentially two parameters can be determined, related to the radium and to the surface thickness. An examination of the Au experiments show that the functional forms of the surface are not important, and that the charge density in the central regions is probably fairly flat, although it cannot be determined very accurately.

Model for the Operation of a Monolayer MoS2 Thin-Film Transistor with Charges Trapped near the Channel Interface

NASA Astrophysics Data System (ADS)

Hur, Ji-Hyun; Park, Junghak; Kim, Deok-kee; Jeon, Sanghun

2017-04-01

We propose a model that describes the operation characteristics of a two-dimensional electron gas (2DEG) in a monolayer transition-metal dichalcogenide thin-film transistor (TFT) having trapped charges near the channel interface. We calculate the drift mobility of the carriers scattered by charged defects located in the channel or near the channel interfaces. The calculated drift mobility is a function of the 2DEG areal density of interface traps. Finally, we calculate the model transfer (ID-VG S ) and output (ID-VS D ) characteristics and verify them by comparing with the experimental results performed with monolayer MoS2 TFTs. We find the modeled results to be excellently consistent with the experiments. This proposed model can be utilized for measuring the interface-trapped charge and trap site densities from the measured transfer curves directly, avoiding more complicated and expensive measurement methods.

Quantum electronic stress: density-functional-theory formulation and physical manifestation.

PubMed

Hu, Hao; Liu, Miao; Wang, Z F; Zhu, Junyi; Wu, Dangxin; Ding, Hepeng; Liu, Zheng; Liu, Feng

2012-08-03

The concept of quantum electronic stress (QES) is introduced and formulated within density functional theory to elucidate extrinsic electronic effects on the stress state of solids and thin films in the absence of lattice strain. A formal expression of QES (σ(QE)) is derived in relation to deformation potential of electronic states (Ξ) and variation of electron density (Δn), σ(QE) = ΞΔn as a quantum analog of classical Hooke's law. Two distinct QES manifestations are demonstrated quantitatively by density functional theory calculations: (1) in the form of bulk stress induced by charge carriers and (2) in the form of surface stress induced by quantum confinement. Implications of QES in some physical phenomena are discussed to underlie its importance.

Extended Lagrangian Density Functional Tight-Binding Molecular Dynamics for Molecules and Solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aradi, Bálint; Niklasson, Anders M. N.; Frauenheim, Thomas

A computationally fast quantum mechanical molecular dynamics scheme using an extended Lagrangian density functional tight-binding formulation has been developed and implemented in the DFTB+ electronic structure program package for simulations of solids and molecular systems. The scheme combines the computational speed of self-consistent density functional tight-binding theory with the efficiency and long-term accuracy of extended Lagrangian Born–Oppenheimer molecular dynamics. Furthermore, for systems without self-consistent charge instabilities, only a single diagonalization or construction of the single-particle density matrix is required in each time step. The molecular dynamics simulation scheme can also be applied to a broad range of problems in materialsmore » science, chemistry, and biology.« less

Extended Lagrangian Density Functional Tight-Binding Molecular Dynamics for Molecules and Solids

DOE PAGES

Aradi, Bálint; Niklasson, Anders M. N.; Frauenheim, Thomas

2015-06-26

A computationally fast quantum mechanical molecular dynamics scheme using an extended Lagrangian density functional tight-binding formulation has been developed and implemented in the DFTB+ electronic structure program package for simulations of solids and molecular systems. The scheme combines the computational speed of self-consistent density functional tight-binding theory with the efficiency and long-term accuracy of extended Lagrangian Born–Oppenheimer molecular dynamics. Furthermore, for systems without self-consistent charge instabilities, only a single diagonalization or construction of the single-particle density matrix is required in each time step. The molecular dynamics simulation scheme can also be applied to a broad range of problems in materialsmore » science, chemistry, and biology.« less

Adsorption of a cationic dye molecule on polystyrene microspheres in colloids: effect of surface charge and composition probed by second harmonic generation.

PubMed

Eckenrode, Heather M; Jen, Shih-Hui; Han, Jun; Yeh, An-Gong; Dai, Hai-Lung

2005-03-17

Nonlinear optical probe, second harmonic generation (SHG), of the adsorption of the dye molecule malachite green (MG), in cationic form at pH < or = 5, on polystyrene microspheres in aqueous solution is used to study the effect of surface charge and composition on molecular adsorption. Three types of polystyrene microspheres with different surface composition are investigated: (1) a sulfate terminated, anionic surface, (2) a neutral surface without any functional group termination, and (3) an amine terminated, cationic surface. The cationic dye was found to adsorb at all three surfaces, regardless of surface charge. The adsorption free energies, DeltaG's, measured for the three surfaces are -12.67, -12.39, and -10.46 kcal/mol, respectively, with the trend as expected from the charge interactions. The adsorption density on the anionic surface, where attractive charge-charge interaction dominates, is determined by the surface negative charge density. The adsorption densities on the neutral and cationic surfaces are on the other hand higher, perhaps as a result of a balance between minimizing repulsive charge interaction and maximizing attractive molecule-substrate and intermolecular interactions. The relative strength of the SH intensity per molecule, in combination of a model calculation, reveals that the C(2) axis of the MG molecule is nearly perpendicular to the surface on the anionic surface and tilts away from the surface norm when the surface is neutral and further away when cationic. Changing the pH of the solution may alter the surface charge and subsequently affect the adsorption configuration and SH intensity.

Electrolyte solutions at curved electrodes. I. Mesoscopic approach

NASA Astrophysics Data System (ADS)

Reindl, Andreas; Bier, Markus; Dietrich, S.

2017-04-01

Within the Poisson-Boltzmann approach, electrolytes in contact with planar, spherical, and cylindrical electrodes are analyzed systematically. The dependences of their capacitance C on the surface charge density σ and the ionic strength I are examined as a function of the wall curvature. The surface charge density has a strong effect on the capacitance for small curvatures, whereas for large curvatures the behavior becomes independent of σ. An expansion for small curvatures gives rise to capacitance coefficients which depend only on a single parameter, allowing for a convenient analysis. The universal behavior at large curvatures can be captured by an analytic expression.

Restoring The Azimuthal Symmetry Of Charged Particle Lateral Density In The Range Of KASCADE-Grande

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sima, O.; Rebel, H.; Apel, W. D.

2010-11-24

KASCADE-Grande, an extension of the former KASCADE experiment, is a multi-component Extensive Air Shower (EAS) experiment located in Karlsruhe Institute of Technology (Campus North), Germany. An important observable for analyzing the EAS is the lateral density of charged particles in the intrinsic shower plane. This observable is deduced from the basic information provided by the Grande scintillators - the energy deposit - first in the observation plane, by using a Lateral Energy Correction Function (LECF), then in the intrinsic shower plane, by applying an adequate mapping procedure. In both steps azimuthal.

Restoring The Azimuthal Symmetry Of Charged Particle Lateral Density In The Range Of KASCADE-Grande

NASA Astrophysics Data System (ADS)

Sima, O.; Rebel, H.; Apel, W. D.; Arteaga, J. C.; Bekk, K.; Bertaina, M.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Buchholz, P.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Engler, J.; Finger, M.; Fuhrmann, D.; Ghia, P. L.; Gils, H. J.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Klages, H. O.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Mayer, H. J.; Melissas, M.; Milke, J.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Oehlschläger, J.; Ostapchenko, S.; Over, S.; Palmieri, N.; Petcu, M.; Pierog, T.; Roth, M.; Schieler, H.; Schröder, F. G.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.

2010-11-01

KASCADE-Grande, an extension of the former KASCADE experiment, is a multi-component Extensive Air Shower (EAS) experiment located in Karlsruhe Institute of Technology (Campus North), Germany. An important observable for analyzing the EAS is the lateral density of charged particles in the intrinsic shower plane. This observable is deduced from the basic information provided by the Grande scintillators-the energy deposit-first in the observation plane, by using a Lateral Energy Correction Function (LECF), then in the intrinsic shower plane, by applying an adequate mapping procedure. In both steps azimuthal.

Vibrational study and Natural Bond Orbital analysis of serotonin in monomer and dimer states by density functional theory

NASA Astrophysics Data System (ADS)

Borah, Mukunda Madhab; Devi, Th. Gomti

2018-06-01

The vibrational spectral analysis of Serotonin and its dimer were carried out using the Fourier Transform Infrared (FTIR) and Raman techniques. The equilibrium geometrical parameters, harmonic vibrational wavenumbers, Frontier orbitals, Mulliken atomic charges, Natural Bond orbitals, first order hyperpolarizability and some optimized energy parameters were computed by density functional theory with 6-31G(d,p) basis set. The detailed analysis of the vibrational spectra have been carried out by computing Potential Energy Distribution (PED, %) with the help of Vibrational Energy Distribution Analysis (VEDA) program. The second order delocalization energies E(2) confirms the occurrence of intramolecular Charge Transfer (ICT) within the molecule. The computed wavenumbers of Serotonin monomer and dimer were found in good agreement with the experimental Raman and IR values.

Charge density wave behavior and order-disorder in the antiferromagnetic metallic series Eu (Ga1 -xAlx)4

NASA Astrophysics Data System (ADS)

Stavinoha, Macy; Cooley, Joya A.; Minasian, Stefan G.; McQueen, Tyrel M.; Kauzlarich, Susan M.; Huang, C.-L.; Morosan, E.

2018-05-01

The solid solution Eu (Ga1-xAlx) 4 was grown in single crystal form to reveal a rich variety of crystallographic, magnetic, and electronic properties that differ from the isostructural end compounds EuGa4 and EuAl4, despite the similar covalent radii and electronic configurations of Ga and Al. Here we report the onset of magnetic spin reorientation and metamagnetic transitions for x =0 -1 evidenced by magnetization and temperature-dependent specific heat measurements. TN changes nonmonotonously with x , and it reaches a maximum around 20 K for x =0.50 , where the a lattice parameter also shows an extreme (minimum) value. Anomalies in the temperature-dependent resistivity consistent with charge density wave behavior exist only for x =0.50 and 1. Density functional theory calculations show increased polarization between the Ga-Al covalent bonds in the x =0.50 structure compared to the end compounds, such that crystallographic order and chemical pressure are proposed as the causes of the charge density wave behavior.

Electronic structure and charge transfer excited states of endohedral fullerene containing electron donoracceptor complexes utilized in organic photovoltaics

NASA Astrophysics Data System (ADS)

Amerikheirabadi, Fatemeh

Organic Donor-Acceptor complexes form the main component of the organic photovoltaic devices (OPVs). The open circuit voltage of OPVs is directly related to the charge transfer excited state energies of these complexes. Currently a large number of different molecular complexes are being tested for their efficiency in photovoltaic devices. In this work, density functional theory as implemented in the NRLMOL code is used to investigate the electronic structure and related properties of these donor-acceptor complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group as the standard time dependent density functional approaches fail to accurately provide them. The model photovoltaics systems analyzed are as follows: Sc3N C 80--ZnTPP, Y3 N C80-- ZnTPP and Sc3 N C80-- ZnPc. In addition, a thorough analysis of the isolated donor and acceptor molecules is also provided. The studied acceptors are chosen from a class of fullerenes named trimetallic nitride endohedral fullerenes. These molecules have shown to possess advantages as acceptors such as long lifetimes of the charge-separated states.

Charge redistribution in QM:QM ONIOM model systems: a constrained density functional theory approach

NASA Astrophysics Data System (ADS)

Beckett, Daniel; Krukau, Aliaksandr; Raghavachari, Krishnan

2017-11-01

The ONIOM hybrid method has found considerable success in QM:QM studies designed to approximate a high level of theory at a significantly reduced cost. This cost reduction is achieved by treating only a small model system with the target level of theory and the rest of the system with a low, inexpensive, level of theory. However, the choice of an appropriate model system is a limiting factor in ONIOM calculations and effects such as charge redistribution across the model system boundary must be considered as a source of error. In an effort to increase the general applicability of the ONIOM model, a method to treat the charge redistribution effect is developed using constrained density functional theory (CDFT) to constrain the charge experienced by the model system in the full calculation to the link atoms in the truncated model system calculations. Two separate CDFT-ONIOM schemes are developed and tested on a set of 20 reactions with eight combinations of levels of theory. It is shown that a scheme using a scaled Lagrange multiplier term obtained from the low-level CDFT model calculation outperforms ONIOM at each combination of levels of theory from 32% to 70%.

Organic heterojunctions: Contact-induced molecular reorientation, interface states, and charge re-distribution

PubMed Central

Opitz, Andreas; Wilke, Andreas; Amsalem, Patrick; Oehzelt, Martin; Blum, Ralf-Peter; Rabe, Jürgen P.; Mizokuro, Toshiko; Hörmann, Ulrich; Hansson, Rickard; Moons, Ellen; Koch, Norbert

2016-01-01

We reveal the rather complex interplay of contact-induced re-orientation and interfacial electronic structure – in the presence of Fermi-level pinning – at prototypical molecular heterojunctions comprising copper phthalocyanine (H16CuPc) and its perfluorinated analogue (F16CuPc), by employing ultraviolet photoelectron and X-ray absorption spectroscopy. For both layer sequences, we find that Fermi-level (EF) pinning of the first layer on the conductive polymer substrate modifies the work function encountered by the second layer such that it also becomes EF-pinned, however, at the interface towards the first molecular layer. This results in a charge transfer accompanied by a sheet charge density at the organic/organic interface. While molecules in the bulk of the films exhibit upright orientation, contact formation at the heterojunction results in an interfacial bilayer with lying and co-facial orientation. This interfacial layer is not EF-pinned, but provides for an additional density of states at the interface that is not present in the bulk. With reliable knowledge of the organic heterojunction’s electronic structure we can explain the poor performance of these in photovoltaic cells as well as their valuable function as charge generation layer in electronic devices. PMID:26887445

Effects of emission layer doping on the spatial distribution of charge and host recombination rate density in organic light emitting devices: A numerical study

NASA Astrophysics Data System (ADS)

Li, Yanli; Zhou, Maoqing; Zheng, Tingcai; Yao, Bo; Peng, Yingquan

2013-12-01

Based on drift-diffusion theory, a numerical model of the doping of a single energy level trap in the emission layer of an organic light emitting device (OLED) was developed, and the effects of doping of this single energy level trap on the distribution of the charge density, the recombination rate density, and the electric field in single- and double-layer OLEDs were studied numerically. The results show that by doping the n-type (p-type) emission layer with single energy electron (hole) traps, the distribution of the recombination rate density can be tuned and shifted, which is useful for improvement of the device performance by reduced electrode quenching or for realization of desirable special functions, e.g., emission spectrum tuning in multiple dye-doped white OLEDs.

Trapped charge densities in Al{sub 2}O{sub 3}-based silicon surface passivation layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jordan, Paul M., E-mail: Paul.Jordan@namlab.com; Simon, Daniel K.; Dirnstorfer, Ingo

2016-06-07

In Al{sub 2}O{sub 3}-based passivation layers, the formation of fixed charges and trap sites can be strongly influenced by small modifications in the stack layout. Fixed and trapped charge densities are characterized with capacitance voltage profiling and trap spectroscopy by charge injection and sensing, respectively. Al{sub 2}O{sub 3} layers are grown by atomic layer deposition with very thin (∼1 nm) SiO{sub 2} or HfO{sub 2} interlayers or interface layers. In SiO{sub 2}/Al{sub 2}O{sub 3} and HfO{sub 2}/Al{sub 2}O{sub 3} stacks, both fixed charges and trap sites are reduced by at least a factor of 5 compared with the value measured inmore » pure Al{sub 2}O{sub 3}. In Al{sub 2}O{sub 3}/SiO{sub 2}/Al{sub 2}O{sub 3} or Al{sub 2}O{sub 3}/HfO{sub 2}/Al{sub 2}O{sub 3} stacks, very high total charge densities of up to 9 × 10{sup 12} cm{sup −2} are achieved. These charge densities are described as functions of electrical stress voltage, time, and the Al{sub 2}O{sub 3} layer thickness between silicon and the HfO{sub 2} or the SiO{sub 2} interlayer. Despite the strong variation of trap sites, all stacks reach very good effective carrier lifetimes of up to 8 and 20 ms on p- and n-type silicon substrates, respectively. Controlling the trap sites in Al{sub 2}O{sub 3} layers opens the possibility to engineer the field-effect passivation in the solar cells.« less

Modeling of Optical Waveguide Poling and Thermally Stimulated Discharge (TSD) Charge and Current Densities for Guest/Host Electro Optic Polymers

NASA Technical Reports Server (NTRS)

Watson, Michael D.; Ashley, Paul R.; Abushagur, Mustafa

2004-01-01

A charge density and current density model of a waveguide system has been developed to explore the effects of electric field electrode poling. An optical waveguide may be modeled during poling by considering the dielectric charge distribution, polarization charge distribution, and conduction charge generated by the poling field. These charge distributions are the source of poling current densities. The model shows that boundary charge current density and polarization current density are the major source of currents measured during poling and thermally stimulated discharge These charge distributions provide insight into the poling mechanisms and are directly related to E(sub A), and, alpha(sub r). Initial comparisons with experimental data show excellent correlation to the model results.

An accurate MOS measurement procedure for work function difference in the Al/SiO 2/Si system

NASA Astrophysics Data System (ADS)

Krautschneider, W. H.; Laschinski, J.; Seifert, W.; Wagemann, H. G.

1986-05-01

Determination of Al/Si work function difference φMS is achieved by means of capacitance measurements of differently manufactured MOS varactors (Al/SiO 2/ n-Si) with variable oxide thickness ("step varactor"). For the φMS evaluation the influences of interface (fQ it) and oxide (ifQ f) charges have been considered, and models of their charges and dipole behaviour are described. Midgap band bending has been chosen as best condition for the evaluation of ΦMSO as basic amount of work function difference with negligible interference of Qit. Plots of Φ MSvs ψS for numerous specimens indicate that, usually, dipole voltage ΔΦ is closely connected to ΦMS within the voltage drop across the MOS varactor according to ΦMS = ΦMSO + qΔΦ. For the evaluation of dipole voltage ΔΦ models of charge density Qit within interface states are presented which assume dominating donor or acceptor states within the two halves of the band gap. Corrections of impurity homogeneity across the wafer and of impurity profile into the depth of the chips are considered. For the work function difference extrapolated to intrinsic density, ΦMSO = (-0.26 ± 0.05) eV holds. Additionally from midgap through inversion of n-Si, dipole voltage was observed ( ΔΦ = 0.015 V) which was caused by interface states and oxide charge 3 nm apart from one another.

Fragment approach to constrained density functional theory calculations using Daubechies wavelets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ratcliff, Laura E.; Genovese, Luigi; Mohr, Stephan

2015-06-21

In a recent paper, we presented a linear scaling Kohn-Sham density functional theory (DFT) code based on Daubechies wavelets, where a minimal set of localized support functions are optimized in situ and therefore adapted to the chemical properties of the molecular system. Thanks to the systematically controllable accuracy of the underlying basis set, this approach is able to provide an optimal contracted basis for a given system: accuracies for ground state energies and atomic forces are of the same quality as an uncontracted, cubic scaling approach. This basis set offers, by construction, a natural subset where the density matrix ofmore » the system can be projected. In this paper, we demonstrate the flexibility of this minimal basis formalism in providing a basis set that can be reused as-is, i.e., without reoptimization, for charge-constrained DFT calculations within a fragment approach. Support functions, represented in the underlying wavelet grid, of the template fragments are roto-translated with high numerical precision to the required positions and used as projectors for the charge weight function. We demonstrate the interest of this approach to express highly precise and efficient calculations for preparing diabatic states and for the computational setup of systems in complex environments.« less

Voltage-Dependent Charge Storage in Cladded Zn0.56Cd0.44Se Quantum Dot MOS Capacitors for Multibit Memory Applications

NASA Astrophysics Data System (ADS)

Khan, J.; Lingalugari, M.; Al-Amoody, F.; Jain, F.

2013-11-01

As conventional memories approach scaling limitations, new storage methods must be utilized to increase Si yield and produce higher on-chip memory density. Use of II-VI Zn0.56Cd0.44Se quantum dots (QDs) is compatible with epitaxial gate insulators such as ZnS-ZnMgS. Voltage-dependent charging effects in cladded Zn0.56Cd0.44Se QDs are presented in a conventional metal-oxide-semiconductor capacitor structure. Charge storage capabilities in Si and ZnMgS QDs have been reported by various researchers; this work is focused on II-VI material Zn0.56Cd0.44Se QDs nucleated using photoassisted microwave plasma metalorganic chemical vapor deposition. Using capacitance-voltage hysteresis characterization, the multistep charging and discharging capabilities of the QDs at room temperature are presented. Three charging states are presented within a 10 V charging voltage range. These characteristics exemplify discrete charge states in the QD layer, perfect for multibit, QD-functionalized high-density memory applications. Multiple charge states with low operating voltage provide device characteristics that can be used for multibit storage by allowing varying charges to be stored in a QD layer based on the applied "write" voltage.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Megala, M.; Rajkumar, Beulah J. M., E-mail: beulah-rajkumar@yahoo.co.in

The electronic and optical transfer properties of Benzene, Benzoic Acid (BA), Nitrobenzene (NB) and Para Nitro Benzoic Acid (PNBA) at ground and first excited state has been investigated by the Density functional theory (DFT)and Time Dependent Density Functional Theory (TDDFT) using SVWN functional/3-21G basis set respectively. Possible intra-molecular charge transfer and n to π* transitions in the ground and the first excitation states have been predicted by the molecular orbitals and the Natural Bond Orbital (NBO) analysis. The simulated absorption spectra have been generated and the result compared with existing experimental results.

Ab-initio study on electronic properties of rocksalt SnAs

NASA Astrophysics Data System (ADS)

Babariya, Bindiya; Vaghela, M. V.; Gajjar, P. N.

2018-05-01

Within the frame work of Local Density Approximation of Exchange and Correlation, ab-initio method of density functional theory with Abinit code is used to compute electronic energy band structure, density of States and charge density of SnAs in rocksalt phase. Our result after optimization for lattice constant agrees with experimental value within 0.59% deviation. The computed electronic energy bands in high symmetry directions Γ→K→X→Γ→L→X→W→L→U shown metallic nature. The lowest band in the electronic band structure is showing band-gap approximately 1.70 eV from next higher band and no crossing between lowest two bands are seen. The density of states revels p-p orbit hybridization between Sn and As atoms. The spherical contour around Sn and As in the charge density plot represent partly ionic and partly covalent bonding. Fermi surface topology is the resultant effect of the single band crossing along L direction at Ef.

Charge-transfer contributions to the excitonic coupling matrix element in BODIPY-based energy transfer cassettes

NASA Astrophysics Data System (ADS)

Spiegel, J. Dominik; Lyskov, Igor; Kleinschmidt, Martin; Marian, Christel M.

2017-01-01

BODIPY-based dyads serve as model systems for the investigation of excitation energy transfer (EET). Through-space EET is brought about by direct and exchange interactions between the transition densities of donor and acceptor localized states. The presence of a molecular linker gives rise to additional charge transfer (CT) contributions. Here, we present a novel approach for the calculation of the excitonic coupling matrix element (ECME) including CT contributions which is based on supermolecular one-electron transition density matrices (STD). The validity of the approach is assessed for a model system of two π -stacked ethylene molecules at varying intermolecular separation. Wave functions and electronic excitation energies of five EET cassettes comprising anthracene as exciton donor and BODIPY as exciton acceptor are obtained by the redesigned combined density functional theory and multireference configuration interaction (DFT/MRCI-R) method. CT contributions to the ECME are shown to be important in the covalently linked EET cassettes.

Intramolecular Charge Transfer States in the Condensed Phase

NASA Astrophysics Data System (ADS)

Williams, C. F.; Herbert, J. M.

2009-06-01

Time-Dependent Density Functional Theory (TDDFT) with long range corrected functionals can give accurate results for the energies of electronically excited states involving Intramolecular Charge Transfer (ICT) in large molecules. If this is combined with a Molecular Mechanics (MM) representation of the surrounding solvent this technique can be used to interpret the results of condensed phase UV-Vis Spectroscopy. Often the MM region is represented by a set of point charges, however this means that the solvent cannot repolarize to adapt to the new charge distribution as a result of ICT and so the excitation energies to ICT states are overestimated. To solve this problem an algorithm that interfaces TDDFT with the polarizable force-field AMOEBA is presented; the effect of solvation on charge transfer in species such as 4,4'dimethylaminobenzonitrile (DMABN) is discussed. M.A. Rohrdanz, K.M. Martins, and J.M. Herbert, J. Chem. Phys. 130 034107 (2008).

Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Changwon; Atalla, Viktor; Smith, Sean

Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

DOE PAGES

Park, Changwon; Atalla, Viktor; Smith, Sean; ...

2017-06-16

Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

Charge transport and magnetization profile at the interface between the correlated metal CaRuO3 and the antiferromagnetic insulator CaMnO3

NASA Astrophysics Data System (ADS)

Freeland, J. W.; Chakhalian, J.; Boris, A. V.; Tonnerre, J.-M.; Kavich, J. J.; Yordanov, P.; Grenier, S.; Zschack, P.; Karapetrova, E.; Popovich, P.; Lee, H. N.; Keimer, B.

2010-03-01

A combination of spectroscopic probes was used to develop a detailed experimental description of the transport and magnetic properties of superlattices composed of the paramagnetic metal CaRuO3 and the antiferromagnetic insulator CaMnO3 . The charge-carrier density and Ru valence state in the superlattices are not significantly different from those of bulk CaRuO3 . The small charge transfer across the interface implied by these observations confirms predictions derived from density-functional calculations. However, a ferromagnetic polarization due to canted Mn spins penetrates 3-4 unit cells into CaMnO3 , far exceeding the corresponding predictions. The discrepancy may indicate the formation of magnetic polarons at the interface.

Polyelectrolyte assisted charge titration spectrometry: Applications to latex and oxide nanoparticles.

PubMed

Mousseau, F; Vitorazi, L; Herrmann, L; Mornet, S; Berret, J-F

2016-08-01

The electrostatic charge density of particles is of paramount importance for the control of the dispersion stability. Conventional methods use potentiometric, conductometric or turbidity titration but require large amount of samples. Here we report a simple and cost-effective method called polyelectrolyte assisted charge titration spectrometry or PACTS. The technique takes advantage of the propensity of oppositely charged polymers and particles to assemble upon mixing, leading to aggregation or phase separation. The mixed dispersions exhibit a maximum in light scattering as a function of the volumetric ratio X, and the peak position XMax is linked to the particle charge density according to σ∼D0XMax where D0 is the particle diameter. The PACTS is successfully applied to organic latex, aluminum and silicon oxide particles of positive or negative charge using poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). The protocol is also optimized with respect to important parameters such as pH and concentration, and to the polyelectrolyte molecular weight. The advantages of the PACTS technique are that it requires minute amounts of sample and that it is suitable to a broad variety of charged nano-objects. Copyright © 2016 Elsevier Inc. All rights reserved.

Proton transfer to charged platinum electrodes. A molecular dynamics trajectory study.

PubMed

Wilhelm, Florian; Schmickler, Wolfgang; Spohr, Eckhard

2010-05-05

A recently developed empirical valence bond (EVB) model for proton transfer on Pt(111) electrodes (Wilhelm et al 2008 J. Phys. Chem. C 112 10814) has been applied in molecular dynamics (MD) simulations of a water film in contact with a charged Pt surface. A total of seven negative surface charge densities σ between -7.5 and -18.9 µC cm(-2) were investigated. For each value of σ, between 30 and 84 initial conditions of a solvated proton within a water slab were sampled, and the trajectories were integrated until discharge of a proton occurred on the charged surfaces. We have calculated the mean rates for discharge and for adsorption of solvated protons within the adsorbed water layer in contact with the metal electrode as a function of surface charge density. For the less negative values of σ we observe a Tafel-like exponential increase of discharge rate with decreasing σ. At the more negative values this exponential increase levels off and the discharge process is apparently transport limited. Mechanistically, the Tafel regime corresponds to a stepwise proton transfer: first, a proton is transferred from the bulk into the contact water layer, which is followed by transfer of a proton to the charged surface and concomitant discharge. At the more negative surface charge densities the proton transfer into the contact water layer and the transfer of another proton to the surface and its discharge occur almost simultaneously.

Electronic doping of transition metal oxide perovskites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cammarata, Antonio, E-mail: cammaant@fel.cvut.cz; Rondinelli, James M.

2016-05-23

CaFeO{sub 3} is a prototypical negative charge transfer oxide that undergoes electronic metal-insulator transition concomitant with a dilation and contraction of nearly rigid octahedra. Altering the charge neutrality of the bulk system destroys the electronic transition, while the structure is significantly modified at high charge content. Using density functional theory simulations, we predict an alternative avenue to modulate the structure and the electronic transition in CaFeO{sub 3}. Charge distribution can be modulated using strain-rotation coupling and thin film engineering strategies, proposing themselves as a promising avenue for fine tuning electronic features in transition metal-oxide perovskites.

Dissociation of methane on the surface of charged defective carbon nanotubes

NASA Astrophysics Data System (ADS)

Guo, Z. H.; Yan, X. H.; Xiao, Y.

2010-03-01

Based on the framework of density functional theory (CASTEP and DMOL 3 codes), we simulate the dissociation of methane (CH 4) molecule on the surface of charged defective carbon nanotubes (CNTs). The results display that a charged CNT with carbon (C) and molybdenum (Mo) dopants can effectively dissociate CH 4 molecule, and the adsorption strength of H and CH 3 can be controlled by the injected negative charges. Moreover, the barrier between the transition state (TS) and the reactant is 0.1014 eV, and a single imaginary frequency of -0.3 cm is found for the transition state structure.

Density-functional expansion methods: Grand challenges.

PubMed

Giese, Timothy J; York, Darrin M

2012-03-01

We discuss the source of errors in semiempirical density functional expansion (VE) methods. In particular, we show that VE methods are capable of well-reproducing their standard Kohn-Sham density functional method counterparts, but suffer from large errors upon using one or more of these approximations: the limited size of the atomic orbital basis, the Slater monopole auxiliary basis description of the response density, and the one- and two-body treatment of the core-Hamiltonian matrix elements. In the process of discussing these approximations and highlighting their symptoms, we introduce a new model that supplements the second-order density-functional tight-binding model with a self-consistent charge-dependent chemical potential equalization correction; we review our recently reported method for generalizing the auxiliary basis description of the atomic orbital response density; and we decompose the first-order potential into a summation of additive atomic components and many-body corrections, and from this examination, we provide new insights and preliminary results that motivate and inspire new approximate treatments of the core-Hamiltonian.

Charge carrier dynamics in organic semiconductors and their donor-acceptor composites: Numerical modeling of time-resolved photocurrent

NASA Astrophysics Data System (ADS)

Johnson, Brian; Kendrick, Mark J.; Ostroverkhova, Oksana

2013-09-01

We present a model that describes nanosecond (ns) time-scale photocurrent dynamics in functionalized anthradithiophene (ADT) films and ADT-based donor-acceptor (D/A) composites. By fitting numerically simulated photocurrents to experimental data, we quantify contributions of multiple pathways of charge carrier photogeneration to the photocurrent, as well as extract parameters that characterize charge transport (CT) in organic films including charge carrier mobilities, trap densities, hole trap depth, and trapping and recombination rates. In pristine ADT films, simulations revealed two competing charge photogeneration pathways: fast, occurring on picosecond (ps) or sub-ps time scales with efficiencies below 10%, and slow, which proceeds at the time scale of tens of nanoseconds, with efficiencies of about 11%-12%, at the applied electric fields of 40-80 kV/cm. The relative contribution of these pathways to the photocurrent was electric field dependent, with the contribution of the fast process increasing with applied electric field. However, the total charge photogeneration efficiency was weakly electric field dependent exhibiting values of 14%-20% of the absorbed photons. The remaining 80%-86% of the photoexcitation did not contribute to charge carrier generation at these time scales. In ADT-based D/A composites with 2 wt.% acceptor concentration, an additional pathway of charge photogeneration that proceeds via CT exciton dissociation contributed to the total charge photogeneration. In the composite with the functionalized pentacene (Pn) acceptor, which exhibits strong exciplex emission from a tightly bound D/A CT exciton, the contribution of the CT state to charge generation was small, ˜8%-12% of the total number of photogenerated charge carriers, dependent on the electric field. In contrast, in the composite with PCBM acceptor, the CT state contributed about a half of all photogenerated charge carriers. In both D/A composites, the charge carrier mobilities were reduced and trap densities and average trap depths were increased, as compared to a pristine ADT donor film. A considerably slower recombination of free holes with trapped electrons was found in the composite with the PCBM acceptor, which led to slower decays of the transient photocurrent and considerably higher charge retention, as compared to a pristine ADT donor film and the composite with the functionalized Pn acceptor.

Conformational study of glyoxal bis(amidinohydrazone) by ab initio methods

NASA Astrophysics Data System (ADS)

Mannfors, B.; Koskinen, J. T.; Pietilä, L.-O.

1997-08-01

We report the first ab initio molecular orbital study on the ground state of the endiamine tautomer of glyoxal bis(amidinohydrazone) (or glyoxal bis(guanylhydrazone), GBG) free base. The calculations were performed at the following levels of theory: Hartree-Fock, second-order Møller-Plesset perturbation theory and density functional theory (B-LYP and B3-LYP) as implemented in the Gaussian 94 software. The standard basis set 6-31G(d) was found to be sufficient. The default fine grid of Gaussian 94 was used in the density functional calculations. Molecular properties, such as optimized structures, total energies and the electrostatic potential derived (CHELPG) atomic charges, were studied as functions of C-C and N-N conformations. The lowest energy conformation was found to be all- trans, in agreement with the experimental solid-state structure. The second conformer with respect to rotation around the central C-C bond was found to be the cis conformer with an MP2//HF energy of 4.67 kcal mol -1. For rotation around the N-N bond the energy increased monotonically from the trans conformation to the cis conformation, the cis energy being very high, 22.01 kcal mol -1 (MP2//HF). The atomic charges were shown to be conformation dependent, and the bond charge increments and especially the conformational changes of the bond charge increments were found to be easily transferable between structurally related systems.

Studies of Ion Beam Charge Neutralization by Ferroelectric Plasma Sources

NASA Astrophysics Data System (ADS)

Stepanov, A.; Gilson, E. P.; Grisham, L.; Davidson, R. C.

2013-10-01

Space-charge forces limit the possible transverse compression of high perveance ion beams that are used in ion-beam-driven high energy density physics applications; the minimum radius to which a beam can be focused is an increasing function of perveance. The limit can be overcome if a plasma is introduced in the beam path between the focusing element and the target in order to neutralize the space charge of the beam. This concept has been implemented on the Neutralized Drift Compression eXperiment (NDCX) at LBNL using Ferroelectric Plasma Sources (FEPS). In our experiment at PPPL, we propagate a perveance-dominated ion beam through a FEPS to study the effect of the neutralizing plasma on the beam envelope and its evolution in time. A 30-60 keV space-charge-dominated Argon beam is focused with an Einzel lens into a FEPS located at the beam waist. The beam is intercepted downstream from the FEPS by a movable Faraday cup that provides time-resolved 2D current density profiles of the beam spot on target. We report results on: (a) dependence of charge neutralization on FEPS plasma density; (b) effects on beam emittance, and (c) time evolution of the beam envelope after the FEPS pulse. Research supported by the U.S. Department of Energy.

Role of carrier density and disorder on anisotropic charge transport in polypyrrole

NASA Astrophysics Data System (ADS)

Varade, Vaibhav; Anjaneyulu, P.; Suchand Sangeeth, C. S.; Ramesh, K. P.; Menon, Reghu

2013-01-01

Polypyrrole (PPy) has been synthesized electrochemically on platinum substrate by varying synthesis temperature and dopant concentration. The charge transport in PPy has been investigated as a function of temperature for both in-plane and out-of-plane geometry in a wide temperature range of 5 K-300 K. The charge transport showed strong anisotropy and various mechanisms were used to explain the transport. The conductivity ratio, σr = σ(300 K)/σ(5 K) is calculated for each sample to quantify the relative disorder. At all the temperatures, the conductivity values for in-plane transport are found to be more for PPy synthesized at lower temperature, while the behavior is found to be different for out-of-plane transport. The carrier density is found to play a crucial role in case of in-plane transport. An effort has been made to correlate charge transport to morphology by analyzing temperature and frequency dependence of conductivity. Charge transport in lateral direction is found to be dominated by hopping whereas tunneling mechanisms are dominated in vertical direction. Parameters such as density of states at the Fermi level [N(EF)], average hopping distance (R), and average hopping energy (W) have been estimated for each samples in both geometry.

Molecular orbital studies (hardness, chemical potential, electronegativity and electrophilicity), vibrational spectroscopic investigation and normal coordinate analysis of 5-{1-hydroxy-2-[(propan-2-yl)amino]ethyl}benzene-1,3-diol.

PubMed

Muthu, S; Renuga, S

2014-01-24

FT-IR and FT-Raman spectra of 5-{1-hydroxy-2-[(propan-2-yl) amino] ethyl} benzene-1,3-diol (abbrevi- 54 ated as HPAEBD) were recorded in the region 4000-450 cm(-1) and 4000-100 cm(-1) respectively. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (B3LYP) and HF method with 6-31 G(d,p) as basis set. The theoretical wave numbers were scaled and compared with experimental FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated Potential energy distribution (PED). Stability of the molecule arising from hyperconjugation and charge delocalization is confirmed by the natural bond orbital analysis (NBO). The results show that electron density (ED) in the σ antibonding orbitals and E (2) energies confirm the occurrence of intra molecular charge transfer (ICT) within the molecule. The molecule orbital contributions were studied by using the total (TDOS), sum of α and β electron (αβDOS) density of States. Mulliken population analysis of atomic charges is also calculated. The calculated HOMO and LUMO energy gap shows that charge transfer occurs within the molecule. The electron density-based local reactivity descriptors such as Fukui functions were calculated to explain the chemical selectivity or reactivity site in this compound. On the basis of vibrational analyses, the thermodynamic properties of title compound at different temperatures have been calculated. Copyright © 2013 Elsevier B.V. All rights reserved.

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

DOE PAGES

Wang, Han; Bang, Junhyeok; Sun, Yiyang; ...

2016-05-10

Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.« less

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Han; Bang, Junhyeok; Sun, Yiyang

Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.« less

The spectroscopic (FTIR, FT-Raman and UV-Vis spectra), DFT and normal coordinate computations of m-nitromethylbenzoate

NASA Astrophysics Data System (ADS)

Gnanasambandan, T.; Gunasekaran, S.; Seshadri, S.

2013-08-01

A combined experimental and theoretical study on molecular structure, vibrational spectra, NBO and UV-spectral analysis of m-nitromethylbenzoate (MNMB) has been reported in the present work. The FT-IR solid phase (4000-400 cm-1) and FT-Raman spectra (3500-100 cm-1) of MNMB was recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of MNMB in the ground-state have been calculated by using the density functional method B3LYP with 6-31G (d,p) and 6-31+G(d,p) basis sets. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). Stability of the molecule arising from hyperconjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ∗ antibonding orbitals and E(2) energies confirms the occurrence of ICT (Intra-molecular Charge Transfer) within the molecule. The UV spectrum was measured in ethyl acetate solution. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) result complements the experimental findings. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Finally the calculation results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra.

Computational insights into charge transfer across functionalized semiconductor surfaces

NASA Astrophysics Data System (ADS)

Kearney, Kara; Rockett, Angus; Ertekin, Elif

2017-12-01

Photoelectrochemical water-splitting is a promising carbon-free fuel production method for producing H2 and O2 gas from liquid water. These cells are typically composed of at least one semiconductor photoelectrode which is prone to degradation and/or oxidation. Various surface modifications are known for stabilizing semiconductor photoelectrodes, yet stabilization techniques are often accompanied by a decrease in photoelectrode performance. However, the impact of surface modification on charge transport and its consequence on performance is still lacking, creating a roadblock for further improvements. In this review, we discuss how density functional theory and finite-element device simulations are reliable tools for providing insight into charge transport across modified photoelectrodes.

Comparative study of charge division in substituted benzene cations

NASA Astrophysics Data System (ADS)

Lee, Kang Taek; Sung, Jiha; Lee, Kwang Jun; Kim, Hyung Min; Han, Kyu Young; Park, Young Dong; Kim, Seong Keun

2007-06-01

A recently proposed phenomenon of charge division in a molecular cation [K. T. Lee et al., J. Am. Chem. Soc. 129, 2588 (2007)] was examined in a number of molecules by experiment and theory. We investigated the spatial distribution of electrostatic charge in the cation of the following benzene derivatives: n-propylbenzene (PB), 3-phenylpropionic acid (PPA), 2-phenylethyl alcohol (PEAL), and 2-phenylethylamine (PEA). A density functional theory calculation indicated that the positive charge was divided into two cationic charge cores in both conformers of PEA+, while it is localized mainly on the phenyl group in PB+, PPA+, and PEAL+. This finding was experimentally verified by the characteristic range of electronic transition of these species reflected in the fragmentation pattern of the mass spectra. The degree of charge division in PEA+ was slightly less than in the cationic conformers of L-phenylalanine in its subgroup II. The charge distribution in a phenyl-containing cation is suggested to depend on whether there exists a functional group that can act as a competing charge core against the phenyl ring.

Self-assembled virus-membrane complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Lihua; Liang, Hongjun; Angelini, Thomas

Anionic polyelectrolytes and cationic lipid membranes can self-assemble into lamellar structures ranging from alternating layers of membranes and polyelectrolytes to 'missing layer' superlattice structures. We show that these structural differences can be understood in terms of the surface-charge-density mismatch between the polyelectrolyte and membrane components by examining complexes between cationic membranes and highly charged M13 viruses, a system that allowed us to vary the polyelectrolyte diameter independently of the charge density. Such virus-membrane complexes have pore sizes that are about ten times larger in area than DNA-membrane complexes, and can be used to package and organize large functional molecules; correlatedmore » arrays of Ru(bpy){sub 3}{sup 2+} macroionic dyes have been directly observed within the virus-membrane complexes using an electron-density reconstruction. These observations elucidate fundamental design rules for rational control of self-assembled polyelectrolyte-membrane structures, which have applications ranging from non-viral gene therapy to biomolecular templates for nanofabrication.« less

Optical ionization detector

DOEpatents

Wuest, C.R.; Lowry, M.E.

1994-03-29

An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium. 3 figures.

Optical ionization detector

DOEpatents

Wuest, Craig R.; Lowry, Mark E.

1994-01-01

An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium.

A density functional theory study on the thermodynamic and dynamic properties of anthraquinone analogue cathode materials for rechargeable lithium ion batteries.

PubMed

Yang, Shu-Jing; Qin, Xiao-Ya; He, Rongxing; Shen, Wei; Li, Ming; Zhao, Liu-Bin

2017-05-21

Organic redox compounds have become the emerging electrode materials for rechargeable lithium ion batteries. The high electrochemical performance provides organic electrode materials with great opportunities to be applied in electric energy storage devices. Among the different types of organic materials, conjugated carbonyl compounds are the most promising type at present, because only they can simultaneously achieve, high energy density, high cycling stability, and high power density. In this research, a series of heteroatom substituted anthraquinone (AQ) derivatives were designed theoretically so that the high theoretical capacity of AQ remained. The discharge and charge mechanism as well as the thermodynamic and dynamic properties of AQ and its derivatives were investigated using first-principles density functional theory. Using heteroatom substitution, both the thermodynamic and dynamic properties of AQ as cathode materials could be largely improved. Among these conjugated carboxyl compounds, BDOZD and BDIOZD with a simultaneously high theoretical capacity and high working potential exhibit the largest energy density of about 780 W h kg -1 , which is 41% larger than that of AQ. The PQD with the smallest value of λ gives the largest charge transfer rate constant, which is about four times as large as the prototype molecule, AQ. The most interesting finding is that the lithium ion transfer plays a very important role in influencing both the discharge potential and electrochemical charge transfer rate. The present study illustrates that theoretical calculations provide a highly effective way to discover potential materials for use with rechargeable lithium ion batteries.

KASCADE-Grande energy reconstruction based on the lateral density distribution using the QGSJet-II.04 interaction model

NASA Astrophysics Data System (ADS)

Gherghel-Lascu, A.; Apel, W. D.; Arteaga-Velázquez, J. C.; Bekk, K.; Bertania, M.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; Di Pierro, F.; Doll, P.; Engel, R.; Fuhrmann, D.; Gils, H. J.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Huber, D.; Huege, T.; Kampert, K.-H.; Kang, D.; Klages, H. O.; Link, K.; Łuczak, P.; Mathes, H. J.; Mayer, H. J.; Milke, J.; Mitrica, B.; Morello, C.; Oehlschläger, J.; Ostapchenko, S.; Palmieri, N.; Pierog, T.; Rebel, H.; Roth, M.; Schieler, H.; Schoo, S.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Weindl, A.; Wochele, J.; Zabierowski, J.

2017-06-01

The charged particle densities obtained from CORSIKA simulated EAS, using the QGSJet-II.04 hadronic interaction model are used for primary energy reconstruction. Simulated data are reconstructed by using Lateral Energy Correction Functions computed with a new realistic model of the Grande stations implemented in Geant4.10.

Valence and charge-transfer optical properties for some SinCm (m, n ≤ 12) clusters: Comparing TD-DFT, complete-basis-limit EOMCC, and benchmarks from spectroscopy

NASA Astrophysics Data System (ADS)

Lutz, Jesse J.; Duan, Xiaofeng F.; Ranasinghe, Duminda S.; Jin, Yifan; Margraf, Johannes T.; Perera, Ajith; Burggraf, Larry W.; Bartlett, Rodney J.

2018-05-01

Accurate optical characterization of the closo-Si12C12 molecule is important to guide experimental efforts toward the synthesis of nano-wires, cyclic nano-arrays, and related array structures, which are anticipated to be robust and efficient exciton materials for opto-electronic devices. Working toward calibrated methods for the description of closo-Si12C12 oligomers, various electronic structure approaches are evaluated for their ability to reproduce measured optical transitions of the SiC2, Si2Cn (n = 1-3), and Si3Cn (n = 1, 2) clusters reported earlier by Steglich and Maier [Astrophys. J. 801, 119 (2015)]. Complete-basis-limit equation-of-motion coupled-cluster (EOMCC) results are presented and a comparison is made between perturbative and renormalized non-iterative triples corrections. The effect of adding a renormalized correction for quadruples is also tested. Benchmark test sets derived from both measurement and high-level EOMCC calculations are then used to evaluate the performance of a variety of density functionals within the time-dependent density functional theory (TD-DFT) framework. The best-performing functionals are subsequently applied to predict valence TD-DFT excitation energies for the lowest-energy isomers of SinC and Sin-1C7-n (n = 4-6). TD-DFT approaches are then applied to the SinCn (n = 4-12) clusters and unique spectroscopic signatures of closo-Si12C12 are discussed. Finally, various long-range corrected density functionals, including those from the CAM-QTP family, are applied to a charge-transfer excitation in a cyclic (Si4C4)4 oligomer. Approaches for gauging the extent of charge-transfer character are also tested and EOMCC results are used to benchmark functionals and make recommendations.

Concentration specific and tunable photoresponse of bismuth vanadate functionalized hexagonal ZnO nanocrystals based photoanodes for photoelectrochemical application

NASA Astrophysics Data System (ADS)

Singh, Sonal; Ruhela, Aakansha; Rani, Sanju; Khanuja, Manika; Sharma, Rishabh

2018-02-01

In the present work, dual layer BiVO4/ZnO photoanode is instigated for photo-electrochemical (PEC) water splitting applications. Two different photocatalytic layers ZnO and BiVO4, reduces charge carrier recombination and charge transfer resistance at photoanode/electrolyte junction. The concentration-specific, tunable and without 'spike and overshoot' features, photocurrent density response is originated by varying BiVO4 concentration in the BiVO4/ZnO photoanode. The crystal structure of ZnO (hexagonal wurtzite structure) and BiVO4 (monoclinic scheelite structure) is confirmed by X-ray diffraction studies. The band gap of BiVO4/ZnO was estimated to be ca. 2.42 eV through Kubler-Munk function F(R∞) using diffuse reflectance spectroscopy. Electrochemical behavior of samples was analyzed with photocurrent measurements, electrochemical impedance, Mott-Schottky plots, bulk separation efficiency and surface transfer efficiency. The maximum photocurrent density of BiVO4/ZnO photoanode was found to be 2.3 times higher than pristine ZnO sample.0.038 M BiVO4/ZnO exhibited the highest separation efficiency of 72% and surface transfer efficiency of 64.7% at +1.23 V vs. RHE. Mott-Schottky study revealed the maximum charge carrier density in the same sample.

Cationic flocculants carrying hydrophobic functionalities: applications for solid/liquid separation.

PubMed

Schwarz, S; Jaeger, W; Paulke, B-R; Bratskaya, S; Smolka, N; Bohrisch, J

2007-07-26

The flocculation behaviors of three series of polycations with narrow molecular weight distributions carrying hydrophobic substituents on their backbones [poly(N-vinylbenzyl-N,N,N-trimethylammonium chloride), poly(N-vinylbenzyl-N,N-dimethyl-N-butylammonium chloride), and poly(N-vinylbenzylpyridinium chloride)] were investigated in dispersions of monodisperse polystyrene latexes and kaolin. Apparently, the charge density of the polycations decreases with increasing substituent hydrophobicity and increasing molecular weight of the polyelectrolytes. The necessary amount of flocculant for phase separation in dispersions with high substrate surface charge densities increases with increasing hydrophobicity of the polyelectrolyte. Nevertheless, the introduction of hydrophobic functionalities is beneficial, resulting in a substantial broadening of the range between the minimum and maximum amounts of flocculant necessary for efficient flocculation (flocculation window). An increase in ionic strength supports this effect. When the substrate has a low charge density, the hydrophobic interactions play a much more significant role in the flocculation process. Here, the minimum efficient doses remained the same for all three polyelectrolytes investigated, but the width of the flocculation window increased as the polycation hydrophobicity and the molecular weight increased. The necessary amount of flocculant increased with an increase in particle size at constant solid content of the dispersion, as well as with a decreasing number of particles at a constant particle size.

KIDS Nuclear Energy Density Functional: 1st Application in Nuclei

NASA Astrophysics Data System (ADS)

Gil, Hana; Papakonstantinou, Panagiota; Hyun, Chang Ho; Oh, Yongseok

We apply the KIDS (Korea: IBS-Daegu-Sungkyunkwan) nuclear energy density functional model, which is based on the Fermi momentum expansion, to the study of properties of lj-closed nuclei. The parameters of the model are determined by the nuclear properties at the saturation density and theoretical calculations on pure neutron matter. For applying the model to the study of nuclei, we rely on the Skyrme force model, where the Skyrme force parameters are determined through the KIDS energy density functional. Solving Hartree-Fock equations, we obtain the energies per particle and charge radii of closed magic nuclei, namely, 16O, 28O, 40Ca, 48Ca, 60Ca, 90Zr, 132Sn, and 208Pb. The results are compared with the observed data and further improvement of the model is shortly mentioned.

An ab-initio study of mechanical, dynamical and electronic properties of MgEu intermetallic

NASA Astrophysics Data System (ADS)

Kumar, S. Ramesh; Jaiganesh, G.; Jayalakshmi, V.

2018-04-01

The theoretical investigation on the mechanical, dynamical and electronic properties of MgEu in CsCl-type structure has been carried out through the ab-initio calculations within the framework of the density functional theory and the density functional perturbation theory. For the purpose, Vienna Ab initio Simulation Package and Phonopy packages were used. Our calculated ground-state properties of MgEu are in good agreement with other available results. Our computed elastic constants and phonon spectrum results suggest that MgEu is mechanically and dynamically stable up to 5 GPa. The thermodynamic quantities as a function of temperatures are also reported and discussed. The band structure, density of states and charge density also calculated to understand the electronic properties of MgEu.

Density-functional expansion methods: evaluation of LDA, GGA, and meta-GGA functionals and different integral approximations.

PubMed

Giese, Timothy J; York, Darrin M

2010-12-28

We extend the Kohn-Sham potential energy expansion (VE) to include variations of the kinetic energy density and use the VE formulation with a 6-31G* basis to perform a "Jacob's ladder" comparison of small molecule properties using density functionals classified as being either LDA, GGA, or meta-GGA. We show that the VE reproduces standard Kohn-Sham DFT results well if all integrals are performed without further approximation, and there is no substantial improvement in using meta-GGA functionals relative to GGA functionals. The advantages of using GGA versus LDA functionals becomes apparent when modeling hydrogen bonds. We furthermore examine the effect of using integral approximations to compute the zeroth-order energy and first-order matrix elements, and the results suggest that the origin of the short-range repulsive potential within self-consistent charge density-functional tight-binding methods mainly arises from the approximations made to the first-order matrix elements.

Nonlinear electron-phonon coupling in doped manganites

DOE PAGES

Esposito, Vincent; Fechner, M.; Mankowsky, R.; ...

2017-06-15

Here, we employ time-resolved resonant x-ray diffraction to study the melting of charge order and the associated insulator-to-metal transition in the doped manganite Pr 0.5Ca 0.5MnO 3 after resonant excitation of a high-frequency infrared-active lattice mode. We find that the charge order reduces promptly and highly nonlinearly as function of excitation fluence. Density-functional theory calculations suggest that direct anharmonic coupling between the excited lattice mode and the electronic structure drives these dynamics, highlighting a new avenue of nonlinear phonon control.

Nonlinear Electron-Phonon Coupling in Doped Manganites.

PubMed

Esposito, V; Fechner, M; Mankowsky, R; Lemke, H; Chollet, M; Glownia, J M; Nakamura, M; Kawasaki, M; Tokura, Y; Staub, U; Beaud, P; Först, M

2017-06-16

We employ time-resolved resonant x-ray diffraction to study the melting of charge order and the associated insulator-to-metal transition in the doped manganite Pr_{0.5}Ca_{0.5}MnO_{3} after resonant excitation of a high-frequency infrared-active lattice mode. We find that the charge order reduces promptly and highly nonlinearly as function of excitation fluence. Density-functional theory calculations suggest that direct anharmonic coupling between the excited lattice mode and the electronic structure drives these dynamics, highlighting a new avenue of nonlinear phonon control.

Density functional theory study of defects in unalloyed δ-Pu

DOE PAGES

Hernandez, S. C.; Freibert, F. J.; Wills, J. M.

2017-03-19

Using density functional theory, we explore in this paper various classical point and complex defects within the face-centered cubic unalloyed δ-plutonium matrix that are potentially induced from self-irradiation. For plutonium only defects, the most energetically stable defect is a distorted split-interstitial. Gallium, the δ-phase stabilizer, is thermodynamically stable as a substitutional defect, but becomes unstable when participating in a complex defect configuration. Finally, complex uranium defects may thermodynamically exist as uranium substitutional with neighboring plutonium interstitial and stabilization of uranium within the lattice is shown via partial density of states and charge density difference plots to be 5f hybridization betweenmore » uranium and plutonium.« less

Density function theory study of the adsorption and dissociation of carbon monoxide on tungsten nanoparticles.

PubMed

Weng, Meng-Hsiung; Ju, Shin-Pon; Chen, Hsin-Tsung; Chen, Hui-Lung; Lu, Jian-Ming; Lin, Ken-Huang; Lin, Jenn-Sen; Hsieh, Jin-Yuan; Yang, Hsi-Wen

2013-02-01

The adsorption and dissociation properties of carbon monoxide (CO) molecule on tungsten W(n) (n = 10-15) nanoparticles have been investigated by density-functional theory (DFT) calculations. The lowest-energy structures for W(n) (n = 10-15) nanoparticles are found by the basin-hopping method and big-bang method with the modified tight-binding many-body potential. We calculated the corresponding adsorption energies, C-O bond lengths and dissociation barriers for adsorption of CO on nanoparticles. The electronic properties of CO on nanoparticles are studied by the analysis of density of state and charge density. The characteristic of CO on W(n) nanoparticles are also compared with that of W bulk.

Density functional theory study of defects in unalloyed δ-Pu

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hernandez, S. C.; Freibert, F. J.; Wills, J. M.

Using density functional theory, we explore in this paper various classical point and complex defects within the face-centered cubic unalloyed δ-plutonium matrix that are potentially induced from self-irradiation. For plutonium only defects, the most energetically stable defect is a distorted split-interstitial. Gallium, the δ-phase stabilizer, is thermodynamically stable as a substitutional defect, but becomes unstable when participating in a complex defect configuration. Finally, complex uranium defects may thermodynamically exist as uranium substitutional with neighboring plutonium interstitial and stabilization of uranium within the lattice is shown via partial density of states and charge density difference plots to be 5f hybridization betweenmore » uranium and plutonium.« less

Current-voltage characteristics influenced by the nanochannel diameter and surface charge density in a fluidic field-effect-transistor.

PubMed

Singh, Kunwar Pal; Guo, Chunlei

2017-06-21

The nanochannel diameter and surface charge density have a significant impact on current-voltage characteristics in a nanofluidic transistor. We have simulated the effect of the channel diameter and surface charge density on current-voltage characteristics of a fluidic nanochannel with positive surface charge on its walls and a gate electrode on its surface. Anion depletion/enrichment leads to a decrease/increase in ion current with gate potential. The ion current tends to increase linearly with gate potential for narrow channels at high surface charge densities and narrow channels are more effective to control the ion current at high surface charge densities. The current-voltage characteristics are highly nonlinear for wide channels at low surface charge densities and they show different regions of current change with gate potential. The ion current decreases with gate potential after attaining a peak value for wide channels at low values of surface charge densities. At low surface charge densities, the ion current can be controlled by a narrow range of gate potentials for wide channels. The current change with source drain voltage shows ohmic, limiting and overlimiting regions.

Classical density functional theory and Monte Carlo simulation study of electric double layer in the vicinity of a cylindrical electrode

NASA Astrophysics Data System (ADS)

Zhou, Shiqi; Lamperski, Stanisław; Sokołowska, Marta

2017-07-01

We have performed extensive Monte-Carlo simulations and classical density functional theory (DFT) calculations of the electrical double layer (EDL) near a cylindrical electrode in a primitive model (PM) modified by incorporating interionic dispersion interactions. It is concluded that (i) in general, an unsophisticated use of the mean field (MF) approximation for the interionic dispersion interactions does not distinctly worsen the classical DFT performance, even if the salt ions considered are highly asymmetrical in size (3:1) and charge (5:1), the bulk molar concentration considered is high up to a total bulk ion packing fraction of 0.314, and the surface charge density of up to 0.5 C m-2. (ii) More specifically, considering the possible noises in the simulation, the local volume charge density profiles are the most accurately predicted by the classical DFT in all situations, and the co- and counter-ion singlet distributions are also rather accurately predicted; whereas the mean electrostatic potential profile is relatively less accurately predicted due to an integral amplification of minor inaccuracy of the singlet distributions. (iii) It is found that the layered structure of the co-ion distribution is abnormally possible only if the surface charge density is high enough (for example 0.5 C m-2) moreover, the co-ion valence abnormally influences the peak height of the first counter-ion layer, which decreases with the former. (iv) Even if both the simulation and DFT indicate an insignificant contribution of the interionic dispersion interaction to the above three ‘local’ quantities, it is clearly shown by the classical DFT that the interionic dispersion interaction does significantly influence a ‘global’ quantity like the cylinder surface-aqueous electrolyte interfacial tension, and this may imply the role of the interionic dispersion interaction in explaining the specific Hofmeister effects. We elucidate all of the above observations based on the arguments from the liquid state theory and at the molecular scale.

Native defects in Tl 6SI 4: Density functional calculations

DOE PAGES

Shi, Hongliang; Du, Mao -Hua

2015-05-05

In this study, Tl 6SI 4 is a promising room-temperature semiconductor radiation detection material. Here, we report density functional calculations of native defects and dielectric properties of Tl 6SI 4. Formation energies and defect levels of native point defects and defect complexes are calculated. Donor-acceptor defect complexes are shown to be abundant in Tl 6SI 4. High resistivity can be obtained by Fermi level pinning by native donor and acceptor defects. Deep donors that are detrimental to electron transport are identified and methods to mitigate such problem are discussed. Furthermore, we show that mixed ionic-covalent character of Tl 6SI 4more » gives rise to enhanced Born effective charges and large static dielectric constant, which provides effective screening of charged defects and impurities.« less

Effect of the surface charge discretization on electric double layers: a Monte Carlo simulation study.

PubMed

Madurga, Sergio; Martín-Molina, Alberto; Vilaseca, Eudald; Mas, Francesc; Quesada-Pérez, Manuel

2007-06-21

The structure of the electric double layer in contact with discrete and continuously charged planar surfaces is studied within the framework of the primitive model through Monte Carlo simulations. Three different discretization models are considered together with the case of uniform distribution. The effect of discreteness is analyzed in terms of charge density profiles. For point surface groups, a complete equivalence with the situation of uniformly distributed charge is found if profiles are exclusively analyzed as a function of the distance to the charged surface. However, some differences are observed moving parallel to the surface. Significant discrepancies with approaches that do not account for discreteness are reported if charge sites of finite size placed on the surface are considered.

Ionic Asymmetry and Solvent Excluded Volume Effects on Spherical Electric Double Layers: A Density Functional Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medasani, Bharat; Ovanesyan, Zaven; Thomas, Dennis G.

In this article we present a classical density functional theory for electrical double layers of spherical macroions that extends the capabilities of conventional approaches by accounting for electrostatic ion correlations, size asymmetry and excluded volume effects. The approach is based on a recent approximation introduced by Hansen-Goos and Roth for the hard sphere excess free energy of inhomogeneous fluids (J. Chem. Phys. 124, 154506). It accounts for the proper and efficient description of the effects of ionic asymmetry and solvent excluded volume, especially at high ion concentrations and size asymmetry ratios including those observed in experimental studies. Additionally, we utilizemore » a leading functional Taylor expansion approximation of the ion density profiles. In addition, we use the Mean Spherical Approximation for multi-component charged hard sphere fluids to account for the electrostatic ion correlation effects. These approximations are implemented in our theoretical formulation into a suitable decomposition of the excess free energy which plays a key role in capturing the complex interplay between charge correlations and excluded volume effects. We perform Monte Carlo simulations in various scenarios to validate the proposed approach, obtaining a good compromise between accuracy and computational cost. We use the proposed computational approach to study the effects of ion size, ion size asymmetry and solvent excluded volume on the ion profiles, integrated charge, mean electrostatic potential, and ionic coordination number around spherical macroions in various electrolyte mixtures. Our results show that both solvent hard sphere diameter and density play a dominant role in the distribution of ions around spherical macroions, mainly for experimental water molarity and size values where the counterion distribution is characterized by a tight binding to the macroion, similar to that predicted by the Stern model.« less

Multiply Reduced Oligofluorenes: Their Nature and Pairing with THF-Solvated Sodium Ions

DOE PAGES

Wu, Qin; Zaikowski, Lori; Kaur, Parmeet; ...

2016-07-01

Conjugated oligofluorenes are chemically reduced up to five charges in tetrahydrofuran solvent and confirmed with clear spectroscopic evidence. Stimulated by these experimental results, we have conducted a comprehensive computational study of the electronic structure and the solvation structure of representative oligofluorene anions with a focus on the pairing between sodium ions and these multianions. In addition, using density functional theory (DFT) methods and a solvation model of both explicit solvent molecules and implicit polarizable continuum, we first elucidate the structure of tightly solvated free sodium ions, and then explore the pairing of sodium ions either in contact with reduced oligofluorenesmore » or as solvent-separated ion pairs. Computed time-dependent-DFT absorption spectra are compared with experiments to assign the dominant ion pairing structure for each multianion. Computed ion pair binding energies further support our assignment. Lastly, the availability of different length and reducing level of oligofluorenes enables us to investigate the effects of total charge and charge density on the binding with sodium ions, and our results suggest both factors play important roles in ion pairing for small molecules. However, as the oligofluorene size grows, its charge density determines the binding strength with the sodium ion.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Qin; Zaikowski, Lori; Kaur, Parmeet

Conjugated oligofluorenes are chemically reduced up to five charges in tetrahydrofuran solvent and confirmed with clear spectroscopic evidence. Stimulated by these experimental results, we have conducted a comprehensive computational study of the electronic structure and the solvation structure of representative oligofluorene anions with a focus on the pairing between sodium ions and these multianions. In addition, using density functional theory (DFT) methods and a solvation model of both explicit solvent molecules and implicit polarizable continuum, we first elucidate the structure of tightly solvated free sodium ions, and then explore the pairing of sodium ions either in contact with reduced oligofluorenesmore » or as solvent-separated ion pairs. Computed time-dependent-DFT absorption spectra are compared with experiments to assign the dominant ion pairing structure for each multianion. Computed ion pair binding energies further support our assignment. Lastly, the availability of different length and reducing level of oligofluorenes enables us to investigate the effects of total charge and charge density on the binding with sodium ions, and our results suggest both factors play important roles in ion pairing for small molecules. However, as the oligofluorene size grows, its charge density determines the binding strength with the sodium ion.« less

The nature of the interaction of dimethylselenide with IIIA group element compounds.

PubMed

Madzhidov, Timur I; Chmutova, Galina A

2013-05-16

The first systematic theoretical study of the nature of intermolecular bonding of dimethylselenide as donor and IIIA group element halides as acceptors was made with the help of the approach of Quantum Theory of Atoms in Molecules. Density Functional Theory with "old" Sapporo triple-ζ basis sets was used to calculate geometry, thermodynamics, and wave function of Me2Se···AX3 complexes. The analysis of the electron density distribution and the Laplacian of the electron density allowed us to reveal and explain the tendencies in the influence of the central atom (A = B, Al, Ga, In) and halogen (X = F, Cl, Br, I) on the nature of Se···A bonding. Significant changes in properties of the selenium lone pair upon complexation were described by means of the analysis of the Laplacian of the charge density. Charge transfer characteristics and the contributions to it from electron localization and delocalization were analyzed in terms of localization and delocalization indexes. Common features of the complexation and differences in the nature of bonding were revealed. Performed analysis evidenced that gallium and indium halide complexes can be attributed to charge transfer-driven complexes; aluminum halides complexes seem to be mainly of an electrostatic nature. The nature of bonding in different boron halides essentially varies; these complexes are stabilized mainly by covalent Se···B interaction. In all the complexes under study covalence of the Se···A interaction is rather high.

Alternative definitions of the frozen energy in energy decomposition analysis of density functional theory calculations.

PubMed

Horn, Paul R; Head-Gordon, Martin

2016-02-28

In energy decomposition analysis (EDA) of intermolecular interactions calculated via density functional theory, the initial supersystem wavefunction defines the so-called "frozen energy" including contributions such as permanent electrostatics, steric repulsions, and dispersion. This work explores the consequences of the choices that must be made to define the frozen energy. The critical choice is whether the energy should be minimized subject to the constraint of fixed density. Numerical results for Ne2, (H2O)2, BH3-NH3, and ethane dissociation show that there can be a large energy lowering associated with constant density orbital relaxation. By far the most important contribution is constant density inter-fragment relaxation, corresponding to charge transfer (CT). This is unwanted in an EDA that attempts to separate CT effects, but it may be useful in other contexts such as force field development. An algorithm is presented for minimizing single determinant energies at constant density both with and without CT by employing a penalty function that approximately enforces the density constraint.

Oriented Covalent Organic Framework Film on Graphene for Robust Ambipolar Vertical Organic Field-Effect Transistor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Bing; Zhu, Chen-Hui; Liu, Yi

Periodically eclipsed π-stacking columns in two-dimensional covalent organic frameworks (2D COFs) could function as direct channel paths for charge carrier transport. Incorporating a welldefined 2D COF into organic electronic devices, however, is still a challenge. Herein, we reported the solvothermal synthesis of a COF TFPy-PPDA film on single layer graphene (SLG), which was constructed via covalent imine-type linkage by employing 1,3,6,8-tetrakis(p-formylphenyl)pyrene (TFPy) and p-phenylenediamine (PPDA) as building blocks. A vertical field-effect transistor (VFET) based on the heterostructure of COF TFPy-PPDA film and SLG shows ambipolar charge carrier behavior under lower modulating voltages. Work-function-tunable contact between SLG and COFTFPy-PPDA film andmore » suitable injection barriers of charge carriers lead to the ambipolar transport with high current density on/off ratio (>10 5) and high on-current density (>4.1 Acm -2). Interfacing 2D COF with graphene for VFET could shed the promising application prospect of 2D COFs in organic electronics and optoelectronics.« less

Charged-particle pseudorapidity distributions in Au+Au collisions at sNN=62.4 GeV

NASA Astrophysics Data System (ADS)

Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Busza, W.; Carroll, A.; Chai, Z.; Decowski, M. P.; García, E.; Gburek, T.; George, N.; Gulbrandsen, K.; Halliwell, C.; Hamblen, J.; Hauer, M.; Henderson, C.; Hofman, D. J.; Hollis, R. S.; Hołyński, R.; Holzman, B.; Iordanova, A.; Johnson, E.; Kane, J. L.; Khan, N.; Kulinich, P.; Kuo, C. M.; Lin, W. T.; Manly, S.; Mignerey, A. C.; Nouicer, R.; Olszewski, A.; Pak, R.; Reed, C.; Roland, C.; Roland, G.; Sagerer, J.; Seals, H.; Sedykh, I.; Smith, C. E.; Stankiewicz, M. A.; Steinberg, P.; Stephans, G. S. F.; Sukhanov, A.; Tonjes, M. B.; Trzupek, A.; Vale, C.; Nieuwenhuizen, G. J. Van; Vaurynovich, S. S.; Verdier, R.; Veres, G. I.; Wenger, E.; Wolfs, F. L. H.; Wosiek, B.; Woźniak, K.; Wysłouch, B.

2006-08-01

The charged-particle pseudorapidity density for Au+Au collisions at sNN=62.4 GeV has been measured over a wide range of impact parameters and compared to results obtained at other energies. As a function of collision energy, the pseudorapidity distribution grows systematically both in height and width. The midrapidity density is found to grow approximately logarithmically between BNL Alternating Gradient Synchrotron (AGS) energies and the top BNL Relativistic Heavy Ion Collider (RHIC) energy. There is also an approximate factorization of the centrality and energy dependence of the midrapidity yields. The new results at sNN=62.4 GeV confirm the previously observed phenomenon of “extended longitudinal scaling” in the pseudorapidity distributions when viewed in the rest frame of one of the colliding nuclei. It is also found that the evolution of the shape of the distribution with centrality is energy independent, when viewed in this reference frame. As a function of centrality, the total charged particle multiplicity scales linearly with the number of participant pairs as it was observed at other energies.

Oriented Covalent Organic Framework Film on Graphene for Robust Ambipolar Vertical Organic Field-Effect Transistor

DOE PAGES

Sun, Bing; Zhu, Chen-Hui; Liu, Yi; ...

2017-04-13

Periodically eclipsed π-stacking columns in two-dimensional covalent organic frameworks (2D COFs) could function as direct channel paths for charge carrier transport. Incorporating a welldefined 2D COF into organic electronic devices, however, is still a challenge. Herein, we reported the solvothermal synthesis of a COF TFPy-PPDA film on single layer graphene (SLG), which was constructed via covalent imine-type linkage by employing 1,3,6,8-tetrakis(p-formylphenyl)pyrene (TFPy) and p-phenylenediamine (PPDA) as building blocks. A vertical field-effect transistor (VFET) based on the heterostructure of COF TFPy-PPDA film and SLG shows ambipolar charge carrier behavior under lower modulating voltages. Work-function-tunable contact between SLG and COFTFPy-PPDA film andmore » suitable injection barriers of charge carriers lead to the ambipolar transport with high current density on/off ratio (>10 5) and high on-current density (>4.1 Acm -2). Interfacing 2D COF with graphene for VFET could shed the promising application prospect of 2D COFs in organic electronics and optoelectronics.« less

Self-Consistent Charge Density Functional Tight-Binding Study of Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) Ammonia Gas Sensor.

PubMed

Marutaphan, Ampaiwan; Seekaew, Yotsarayuth; Wongchoosuk, Chatchawal

2017-12-01

Geometric and electronic properties of 3,4-ethylenedioxythiophene (EDOT), styrene sulfonate (SS), and EDOT: SS oligomers up to 10 repeating units were studied by the self-consistent charge density functional tight-binding (SCC-DFTB) method. An application of PEDOT:PSS for ammonia (NH 3 ) detection was highlighted and investigated both experimentally and theoretically. The results showed an important role of H-bonds in EDOT:SS oligomers complex conformation. Electrical conductivity of EDOT increased with increasing oligomers and doping SS due to enhancement of π conjugation. Printed PEDOT:PSS gas sensor exhibited relatively high response and selectivity to NH 3 . The SCC-DFTB calculation suggested domination of direct charge transfer process in changing of PEDOT:PSS conductivity upon NH 3 exposure at room temperature. The NH 3 molecules preferred to bind with PEDOT:PSS via physisorption. The most favorable adsorption site for PEDOT:PSS-NH 3 interaction was found to be at the nitrogen atom of NH 3 and hydrogen atoms of SS with an average optimal binding distance of 2.00 Å.

Structure and Electronic Properties of Neutral and Negatively Charged RhBn Clusters (n = 3-10): A Density Functional Theory Study.

PubMed

Li, Peifang; Mei, Tingting; Lv, Linxia; Lu, Cheng; Wang, Weihua; Bao, Gang; Gutsev, Gennady L

2017-08-31

The geometrical structure and electronic properties of the neutral RhB n and singly negatively charged RhB n - clusters are obtained in the range of 3 ≤ n ≤ 10 using the unbiased CALYPSO structure search method and density functional theory (DFT). A combination of the PBE0 functional and the def2-TZVP basis set is used for determining global minima on potential energy surfaces of the Rh-doped B n clusters. The photoelectron spectra of the anions are simulated using the time-dependent density functional theory (TD-DFT) method. Good agreement between our simulated and experimentally obtained photoelectron spectra for RhB 9 - provides support to the validity of our theoretical method. The relative stabilities of the ground-state RhB n and RhB n - clusters are estimated using the calculated binding energies, second-order total energy differences, and HOMO-LUMO gaps. It is found that RhB 7 and RhB 8 - are the most stable species in the neutral and anionic series, respectively. The chemical bonding analysis reveals that the RhB 8 - cluster possesses two sets of delocalized σ and π bonds. In both cases, the Hückel 4N + 2 rule is fulfilled and this cluster possesses both σ and π aromaticities.

Spectroscopic studies (FT-IR, FT-Raman, UV-Visible), normal co-ordinate analysis, first-order hyperpolarizability and HOMO, LUMO studies of 3,4-dichlorobenzophenone by using Density Functional Methods.

PubMed

Venkata Prasad, K; Samatha, K; Jagadeeswara Rao, D; Santhamma, C; Muthu, S; Mark Heron, B

2015-01-01

The vibrational frequencies of 3,4-dichlorobenzophenone (DCLBP) were obtained from the FT-IR and Raman spectral data, and evaluated based on the Density Functional Theory using the standard method B3LYP with 6-311+G(d,p) as the basis set. On the basis of potential energy distribution together with the normal-co-ordinate analysis and following the scaled quantum mechanical force methodology, the assignments for the various frequencies were described. The values of the electric dipole moment (μ) and the first-order hyperpolarizability (β) of the molecule were computed. The UV-absorption spectrum was also recorded to study the electronic transitions. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The NBO analysis, to study the intramolecular hyperconjugative interactions, was carried out. Mulliken's net charges were evaluated. The MEP and thermodynamic properties were also calculated. The electron density-based local reactivity descriptor, such as Fukui functions, was calculated to explain the chemical selectivity or reactivity site in 3,4-dichlorobenzophenone. Copyright © 2015 Elsevier B.V. All rights reserved.

Electronic and magnetic properties of transition metal doped graphyne

NASA Astrophysics Data System (ADS)

Gangan, Abhijeet Sadashiv; Yadav, Asha S.; Chakraborty, Brahmananda; Ramaniah, Lavanya M.

2017-05-01

We have theoretically investigated the interaction of few 3d (V,Mn) and 4d (Y,Zr) transition metals with the γ-graphyne structure using the spin-polarized density functional theory for its potentials application in Hydrogen storage, spintronics and nano-electronics. By doping different TMs we have observed that the system can be either metallic(Y), semi-conducting or half metallic. The system for Y and Zr doped graphyne becomes non-magnetic while V and Mn doped graphyne have a magnetic moments of l μB and 3 μB respectively From bader charge analysis it is seen that there is a charge transfer from the TM atom to the graphyne. Zr and Y have a net charge transfer of 2.15e and 1.73e respectively. Charge density analysis also shows the polarization on the carbon skeleton which becomes larger as the charge transfer for the TM atom increases. Thus we see Y and Zr are better candidates for hydrogen storage devices since they are non-magnetic and have less d electrons which is ideal for kubas-type interactions between hydrogen molecule and TM.

Charge delocalization characteristics of regioregular high mobility polymers

DOE PAGES

Coughlin, J. E.; Zhugayevych, A.; Wang, M.; ...

2017-01-01

Controlling the regioregularity among the structural units of narrow bandgap conjugated polymer backbones has led to improvements in optoelectronic properties, for example in the mobilities observed in field effect transistor devices. To investigate how the regioregularity affects quantities relevant to hole transport, regioregular and regiorandom oligomers representative of polymeric structures were studied using density functional theory. Several structural and electronic characteristics of the oligomers were compared, including chain planarity, cation spin density, excess charges on molecular units and internal reorganizational energy. The main difference between the regioregular and regiorandom oligomers is found to be the conjugated backbone planarity, while themore » reorganizational energies calculated are quite similar across the molecular family. Lastly, this work constitutes the first step on understanding the complex interplay of atomistic changes and an oligomer backbone structure toward modeling the charge transport properties.« less

Charge transport and magnetization profile at the interface between the correlated metal CaRuO3 and the antiferromagnetic insulator CaMnO3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Freeland, J. W.; Chakhalian, J.; Boris, A. V.

2010-01-01

A combination of spectroscopic probes was used to develop a detailed experimental description of the transport and magnetic properties of superlattices composed of the paramagnetic metal CaRuO3 and the antiferromagnetic insulator CaMnO3. The charge carrier density and Ru valence state in the superlattices are not significantly different from those of bulk CaRuO3. The small charge transfer across the interface implied by these observations confirms predictions derived from density functional calculations. However, a ferromagnetic polarization due to canted Mn spins penetrates 3-4 unit cells into CaMnO3, far exceeding the corresponding predictions. The discrepancy may indicate the formation of magnetic polarons atmore » the interface.« less

Charge density wave order in 1D mirror twin boundaries of single-layer MoSe 2

DOE PAGES

Barja, Sara; Wickenburg, Sebastian; Liu, Zhen-Fei; ...

2016-04-18

Here, We provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries (MTBs) of single-layer semiconducting MoSe 2. Such MTBs have been previously observed by transmission electron microscopy and have been predicted to be metallic in MoSe 2 and MoS 2. Our low-temperature scanning tunnelling microscopy/spectroscopy measurements revealed a substantial bandgap of 100 meV opening at the Fermi energy in the otherwise metallic one-dimensional structures. We found a periodic modulation in the density of states along the MTB, with a wavelength of approximately three lattice constants. In addition to mapping the energy-dependent densitymore » of states, we determined the atomic structure and bonding of the MTB through simultaneous high-resolution non-contact atomic force microscopy. Density functional theory calculations based on the observed structure reproduced both the gap opening and the spatially resolved density of states.« less

Green's function enriched Poisson solver for electrostatics in many-particle systems

NASA Astrophysics Data System (ADS)

Sutmann, Godehard

2016-06-01

A highly accurate method is presented for the construction of the charge density for the solution of the Poisson equation in particle simulations. The method is based on an operator adjusted source term which can be shown to produce exact results up to numerical precision in the case of a large support of the charge distribution, therefore compensating the discretization error of finite difference schemes. This is achieved by balancing an exact representation of the known Green's function of regularized electrostatic problem with a discretized representation of the Laplace operator. It is shown that the exact calculation of the potential is possible independent of the order of the finite difference scheme but the computational efficiency for higher order methods is found to be superior due to a faster convergence to the exact result as a function of the charge support.

Metal-Free Multiple Carbon-Carbon and Carbon-Hydrogen Bond Activations via Charge-Switching Mechanism in Unstrained Diindolylmethanes.

PubMed

Challa, Chandrasekhar; Varughese, Sunil; Suresh, Cherumuttathu H; Lankalapalli, Ravi S

2017-08-18

A transformation of the unstrained phenol substituted 3,3'-diindolylmethanes (DIPMs) to 2,3'-diindolylketones (DIKs) by double C-C single bond cleavage with associated rearrangements, triggered by phenyliodine(III) diacetate (PIDA), is reported. Density functional theory studies reveal a mechanism involving multiple "charge-switching" steps by synergistic involvement of the two indole units with overall low activation energy. The indole 'charge-switching' mechanism in DIPMs was further extended toward synthesis of a natural product motif cyclohepta[b]indole from biaryl appended DIBM.

Defect charge states in Si doped hexagonal boron-nitride monolayer

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Molepo, M. P.; Andrew, R. C.; Chetty, N.

2016-02-01

We perform ab initio density functional theory calculations to investigate the energetics, electronic and magnetic properties of isolated stoichiometric and non-stoichiometric substitutional Si complexes in a hexagonal boron-nitride monolayer. The Si impurity atoms substituting the boron atom sites SiB giving non-stoichiometric complexes are found to be the most energetically favourable, and are half-metallic and order ferromagnetically in the neutral charge state. We find that the magnetic moments and magnetization energies increase monotonically when Si defects form a cluster. Partial density of states and standard Mulliken population analysis indicate that the half-metallic character and magnetic moments mainly arise from the Si 3p impurity states. The stoichiometric Si complexes are energetically unfavorable and non-magnetic. When charging the energetically favourable non-stoichiometric Si complexes, we find that the formation energies strongly depend on the impurity charge states and Fermi level position. We also find that the magnetic moments and orderings are tunable by charge state modulation q  =  -2, -1, 0, +1, +2. The induced half-metallic character is lost (retained) when charging isolated (clustered) Si defect(s). This underlines the potential of a Si doped hexagonal boron-nitride monolayer for novel spin-based applications.

Investigation of Oxygen and Hydrogen Associated Charge Trapping and Electrical Characteristics of Silicon Nitride Films for Mnos Devices.

NASA Astrophysics Data System (ADS)

Xu, Dan

Silicon nitride (Si_3N _4) and silicon oxynitride (SiO _{rm x}N_ {rm y}) films in the form of metal -nitride-oxide-silicon (MNOS) structures were investigated to determine the correlation between their electrical characteristics and the nature of the chemical bonding so as to provide guidelines for the next generation of nonvolatile memory devices. The photoionization cross section of electron traps in the oxynitride films of MNOS devices were also measured as a function photon energy and oxygen concentration of the silicon oxynitride films. An effective photoionization cross section associated with electron traps was determined to be between 4.9 times 10 ^{-19} cm^2 to 10.8 times 10^ {-19} cm^2 over the photon energy of 2.06 eV to 3.1 eV for silicon oxynitride films containing 7 atomic % to 17 atomic % of oxygen. The interface state density of metal-nitride-oxide -silicon (MNOS) devices was investigated as a function of processing conditions. The interface state density around the midgap of the oxide-silicon interface of the MNOS structures for deposition temperature between 650^ circC to 850^circC increased from 1.1 to 8.2 times 10 ^{11} cm^ {-2}eV^{-1}, for as-deposited silicon nitride films; but decreased from 5.0 to 3.5 times 10^ {11} cm^{-2} eV^{-1}, for films annealed in nitrogen at 900^circC for 60 minutes; and further decreased and remained constant at 1.5 times 10^{11 } cm^{-2}eV ^{-1}, for films which were further annealed in hydrogen at 900^ circC for an additional 60 minutes. The interface state density increase was due to an increase in the loss of hydrogen at the interfacial region and also due to an increase in the thermal stress caused by differences in thermal expansion coefficients of silicon nitride and silicon dioxide films at higher deposition temperatures. The interface state density was subject to two opposing influences; an increase by thermal stress, and a reduction by hydrogen compensation of these states. The photocurrent-voltage (photoI-V) technique in combination with internal photo-electric technique were employed to determine the trapped charge density and its centroid as a function of processing conditions. Results showed that the trapped charge density was of the order of 10^{18} cm ^{-3}. However, the charge trapping density increased about 30% as the atomic percentage of hydrogen decreased from 6 to 2 atomic %.

Vertex functions at finite momentum: Application to antiferromagnetic quantum criticality

NASA Astrophysics Data System (ADS)

Wölfle, Peter; Abrahams, Elihu

2016-02-01

We analyze the three-point vertex function that describes the coupling of fermionic particle-hole pairs in a metal to spin or charge fluctuations at nonzero momentum. We consider Ward identities, which connect two-particle vertex functions to the self-energy, in the framework of a Hubbard model. These are derived using conservation laws following from local symmetries. The generators considered are the spin density and particle density. It is shown that at certain antiferromagnetic critical points, where the quasiparticle effective mass is diverging, the vertex function describing the coupling of particle-hole pairs to the spin density Fourier component at the antiferromagnetic wave vector is also divergent. Then we give an explicit calculation of the irreducible vertex function for the case of three-dimensional antiferromagnetic fluctuations, and show that it is proportional to the diverging quasiparticle effective mass.

Ab initio calculation of the potential bubble nucleus 34Si

NASA Astrophysics Data System (ADS)

Duguet, T.; Somà, V.; Lecluse, S.; Barbieri, C.; Navrátil, P.

2017-03-01

Background: The possibility that an unconventional depletion (referred to as a "bubble") occurs in the center of the charge density distribution of certain nuclei due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. Based on a mean-field rationale, a correlation between the occurrence of such a semibubble and an anomalously weak splitting between low angular-momentum spin-orbit partners has been further conjectured. Energy density functional and valence-space shell model calculations have been performed to identify and characterize the best candidates, among which 34Si appears as a particularly interesting case. While the experimental determination of the charge density distribution of the unstable 34Si is currently out of reach, (d ,p ) experiments on this nucleus have been performed recently to test the correlation between the presence of a bubble and an anomalously weak 1 /2--3 /2- splitting in the spectrum of 35Si as compared to 37S. Purpose: We study the potential bubble structure of 34Si on the basis of the state-of-the-art ab initio self-consistent Green's function many-body method. Methods: We perform the first ab initio calculations of 34Si and 36S. In addition to binding energies, the first observables of interest are the charge density distribution and the charge root-mean-square radius for which experimental data exist in 36S. The next observable of interest is the low-lying spectroscopy of 35Si and 37S obtained from (d ,p ) experiments along with the spectroscopy of 33Al and 35P obtained from knock-out experiments. The interpretation in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input internucleon interactions. The convergence of the results with respect to the truncation of the many-body expansion, i.e., with respect to the many-body correlations included in the calculation, is studied in detail. We eventually compare our predictions to state-of-the-art multireference energy density functional and shell model calculations. Results: The prediction regarding the (non)existence of the bubble structure in 34Si varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root-mean-square radius of 36S be well reproduced, along with 34Si and 36S binding energies, only leaves the NNLOsat Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of 34Si, is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1 /2--3 /2- splitting in the spectrum of 35Si as compared to 37S. Conclusions: The occurrence of a bubble structure in the charge distribution of 34Si is convincingly established on the basis of state-of-the-art ab initio calculations. This prediction will have to be reexamined in the future when improved chiral nuclear Hamiltonians are constructed. On the experimental side, present results act as a strong motivation to measure the charge density distribution of 34Si in future electron scattering experiments on unstable nuclei. In the meantime, it is of interest to perform one-neutron removal on 34Si and 36S in order to further test our theoretical spectral strength distributions over a wide energy range.

Vibrational spectroscopic investigation and normal coordinate analysis of the fibrate hypolipidemic agent 5-(2,5-dimethylphenoxy)-2,2-dimethyl pentanoic acid (Gemfibrozil)

NASA Astrophysics Data System (ADS)

Priya, M. Siva; Benitta, T. Asenath; James, C.

2011-03-01

Colorless crystals of 5-(2,5-dimethylphenoxy)-2,2-dimethyl pentanoic acid were grown by slow evaporation method and the FT-IR and FT-Raman spectra of the sample were recorded in the region 4000-450 cm -1 and 4000-50 cm -1 respectively. Molecular structure is optimized with the help of B3LYP/6-31G (d) density functional theory method. Stability of the molecule arising from hyperconjugation and charge delocalization is confirmed by the natural bond orbital analysis (NBO). The results show that electron density (ED) in the σ ∗ antibonding orbitals and E (2) energies confirms the occurrence of intra-molecular charge transfer (ICT) within the molecule. The assignments of the vibrational spectra have been carried out with the help of Normal coordinate analysis following the scaled quantum mechanical force field (SQMFF) methodology. Mulliken population analysis on atomic charges is also calculated. The calculated HOMO and LUMO energy gap shows that charge transfer occurs within the molecule.

Induced Charge Fluctuations in Semiconductor Detectors with a Cylindrical Geometry

NASA Astrophysics Data System (ADS)

Samedov, Victor V.

2018-01-01

Now, compound semiconductors are very appealing for hard X-ray room-temperature detectors for medical and astrophysical applications. Despite the attractive properties of compound semiconductors, such as high atomic number, high density, wide band gap, low chemical reactivity and long-term stability, poor hole and electron mobility-lifetime products degrade the energy resolution of these detectors. The main objective of the present study is in development of a mathematical model of the process of the charge induction in a cylindrical geometry with accounting for the charge carrier trapping. The formulae for the moments of the distribution function of the induced charge and the formulae for the mean amplitude and the variance of the signal at the output of the semiconductor detector with a cylindrical geometry were derived. It was shown that the power series expansions of the detector amplitude and the variance in terms of the inverse bias voltage allow determining the Fano factor, electron mobility lifetime product, and the nonuniformity level of the trap density of the semiconductor material.

Method for Estimating the Charge Density Distribution on a Dielectric Surface.

PubMed

Nakashima, Takuya; Suhara, Hiroyuki; Murata, Hidekazu; Shimoyama, Hiroshi

2017-06-01

High-quality color output from digital photocopiers and laser printers is in strong demand, motivating attempts to achieve fine dot reproducibility and stability. The resolution of a digital photocopier depends on the charge density distribution on the organic photoconductor surface; however, directly measuring the charge density distribution is impossible. In this study, we propose a new electron optical instrument that can rapidly measure the electrostatic latent image on an organic photoconductor surface, which is a dielectric surface, as well as a novel method to quantitatively estimate the charge density distribution on a dielectric surface by combining experimental data obtained from the apparatus via a computer simulation. In the computer simulation, an improved three-dimensional boundary charge density method (BCM) is used for electric field analysis in the vicinity of the dielectric material with a charge density distribution. This method enables us to estimate the profile and quantity of the charge density distribution on a dielectric surface with a resolution of the order of microns. Furthermore, the surface potential on the dielectric surface can be immediately calculated using the obtained charge density. This method enables the relation between the charge pattern on the organic photoconductor surface and toner particle behavior to be studied; an understanding regarding the same may lead to the development of a new generation of higher resolution photocopiers.

Modeling solvation effects in real-space and real-time within density functional approaches

NASA Astrophysics Data System (ADS)

Delgado, Alain; Corni, Stefano; Pittalis, Stefano; Rozzi, Carlo Andrea

2015-10-01

The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the Octopus code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water.

Modeling solvation effects in real-space and real-time within density functional approaches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delgado, Alain; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear, Calle 30 # 502, 11300 La Habana; Corni, Stefano

2015-10-14

The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that aremore » close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the OCTOPUS code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water.« less

Charge Transport Properties of Durene Crystals from First-Principles.

PubMed

Motta, Carlo; Sanvito, Stefano

2014-10-14

We establish a rigorous computational scheme for constructing an effective Hamiltonian to be used for the determination of the charge carrier mobility of pure organic crystals at finite temperature, which accounts for van der Waals interactions, and it includes vibrational contributions from the entire phonon spectrum of the crystal. Such an approach is based on the ab initio framework provided by density functional theory and the construction of a tight-binding effective model via Wannier transformation. The final Hamiltonian includes coupling of the electrons to the crystals phonons, which are also calculated from density functional theory. We apply this methodology to the case of durene, a small π-conjugated molecule, which forms a high-mobility herringbone-stacked crystal. We show that accounting correctly for dispersive forces is fundamental for obtaining a high-quality phonon spectrum, in agreement with experiments. Then, the mobility as a function of temperature is calculated along different crystallographic directions and the phonons most responsible for the scattering are identified.

Intrinsic point defects in β-In2S3 studied by means of hybrid density-functional theory

NASA Astrophysics Data System (ADS)

Ghorbani, Elaheh; Albe, Karsten

2018-03-01

We have employed first principles total energy calculations in the framework of density functional theory, with plane wave basis sets and screened exchange hybrid functionals to study the incorporation of intrinsic defects in bulk β-In2S3. The results are obtained for In-rich and S-rich experimental growth conditions. The charge transition level is discussed for all native defects, including VIn, VS, Ini, Si, SIn, and InS, and a comparison between the theoretically calculated charge transition levels and the available experimental findings is presented. The results imply that β-In2S3 shows n-type conductivity under both In-rich and S-rich growth conditions. The indium antiisite (InS), the indium interstitial (Ini), and the sulfur vacancy ( VS ' ) are found to be the leading sources of sample's n-type conductivity. When going from the In-rich to the S-rich condition, the conductivity of the material decreases; however, the type of conductivity remains unchanged.

Ising tricriticality in the extended Hubbard model with bond dimerization

NASA Astrophysics Data System (ADS)

Fehske, Holger; Ejima, Satoshi; Lange, Florian; Essler, Fabian H. L.

We explore the quantum phase transition between Peierls and charge-density-wave insulating states in the one-dimensional, half-filled, extended Hubbard model with explicit bond dimerization. We show that the critical line of the continuous Ising transition terminates at a tricritical point, belonging to the universality class of the tricritical Ising model with central charge c=7/10. Above this point, the quantum phase transition becomes first order. Employing a numerical matrix-product-state based (infinite) density-matrix renormalization group method we determine the ground-state phase diagram, the spin and two-particle charge excitations gaps, and the entanglement properties of the model with high precision. Performing a bosonization analysis we can derive a field description of the transition region in terms of a triple sine-Gordon model. This allows us to derive field theory predictions for the power-law (exponential) decay of the density-density (spin-spin) and bond-order-wave correlation functions, which are found to be in excellent agreement with our numerical results. This work was supported by Deutsche Forschungsgemeinschaft (Germany), SFB 652, project B5, and by the EPSRC under Grant No. EP/N01930X/1 (FHLE).

Charge-transfer channel in quantum dot-graphene hybrid materials

NASA Astrophysics Data System (ADS)

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-01

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd13Se13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Charge-transfer channel in quantum dot-graphene hybrid materials.

PubMed

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-06

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd 13 Se 13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Density of Trap States and Auger-mediated Electron Trapping in CdTe Quantum-Dot Solids.

PubMed

Boehme, Simon C; Azpiroz, Jon Mikel; Aulin, Yaroslav V; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Infante, Ivan; Houtepen, Arjan J

2015-05-13

Charge trapping is an ubiquitous process in colloidal quantum-dot solids and a major limitation to the efficiency of quantum dot based devices such as solar cells, LEDs, and thermoelectrics. Although empirical approaches led to a reduction of trapping and thereby efficiency enhancements, the exact chemical nature of the trapping mechanism remains largely unidentified. In this study, we determine the density of trap states in CdTe quantum-dot solids both experimentally, using a combination of electrochemical control of the Fermi level with ultrafast transient absorption and time-resolved photoluminescence spectroscopy, and theoretically, via density functional theory calculations. We find a high density of very efficient electron traps centered ∼0.42 eV above the valence band. Electrochemical filling of these traps increases the electron lifetime and the photoluminescence quantum yield by more than an order of magnitude. The trapping rate constant for holes is an order of magnitude lower that for electrons. These observations can be explained by Auger-mediated electron trapping. From density functional theory calculations we infer that the traps are formed by dicoordinated Te atoms at the quantum dot surface. The combination of our unique experimental determination of the density of trap states with the theoretical modeling of the quantum dot surface allows us to identify the trapping mechanism and chemical reaction at play during charge trapping in these quantum dots.

Complexation of ferric oxide particles with pectins of different charge density.

PubMed

Milkova, Viktoria; Kamburova, Kamelia; Petkanchin, Ivana; Radeva, Tsetska

2008-09-02

The effect of polyelectrolyte charge density on the electrical properties and stability of suspensions of oppositely charged oxide particles is followed by means of electro-optics and electrophoresis. Variations in the electro-optical effect and the electrophoretic mobility are examined at conditions where fully ionized pectins of different charge density adsorb onto particles with ionizable surfaces. The charge neutralization point coincides with the maximum of particle aggregation in all suspensions. We find that the concentration of polyelectrolyte, needed to neutralize the particle charge, decreases with increasing charge density of the pectin. The most highly charged pectin presents an exception to this order, which is explained with a reduction of the effective charge density of this pectin due to condensation of counterions. The presence of condensed counterions, remaining bound to the pectin during its adsorption on the particle surface, is proved by investigation of the frequency behavior of the electro-optical effect at charge reversal of the particle surface.

A method to estimate statistical errors of properties derived from charge-density modelling

PubMed Central

Lecomte, Claude

2018-01-01

Estimating uncertainties of property values derived from a charge-density model is not straightforward. A methodology, based on calculation of sample standard deviations (SSD) of properties using randomly deviating charge-density models, is proposed with the MoPro software. The parameter shifts applied in the deviating models are generated in order to respect the variance–covariance matrix issued from the least-squares refinement. This ‘SSD methodology’ procedure can be applied to estimate uncertainties of any property related to a charge-density model obtained by least-squares fitting. This includes topological properties such as critical point coordinates, electron density, Laplacian and ellipticity at critical points and charges integrated over atomic basins. Errors on electrostatic potentials and interaction energies are also available now through this procedure. The method is exemplified with the charge density of compound (E)-5-phenylpent-1-enylboronic acid, refined at 0.45 Å resolution. The procedure is implemented in the freely available MoPro program dedicated to charge-density refinement and modelling. PMID:29724964

Current Flow and Pair Creation at Low Altitude in Rotation-Powered Pulsars' Force-Free Magnetospheres: Space Charge Limited Flow

NASA Technical Reports Server (NTRS)

Timokhin, A. N.; Arons, J.

2013-01-01

We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of rotation-powered pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, including a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte Carlo treatment of the high-energy gamma-rays that mediate the formation of the electron-positron pairs.We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially one dimensional, and designed to explore the physics, although of practical relevance to young, high-voltage pulsars. We observe novel behaviour (a) When the current density j is less than the Goldreich-Julian value (0 < j/j(sub GJ) < 1), space charge limited acceleration of the current carrying beam is mild, with the full Goldreich-Julian charge density comprising the charge densities of the beam and a cloud of electrically trapped particles with the same sign of charge as the beam. The voltage drops are of the order of mc(sup 2)/e, and pair creation is absent. (b) When the current density exceeds the Goldreich-Julian value (j/j(sub GJ) > 1), the system develops high voltage drops (TV or greater), causing emission of curvature gamma-rays and intense bursts of pair creation. The bursts exhibit limit cycle behaviour, with characteristic time-scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). (c) In return current regions, where j/j(sub GJ) < 0, the system develops similar bursts of pair creation. These discharges are similar to those encountered in previous calculations by Timokhin of pair creation when the surface has a high work function and cannot freely emit charge. In cases (b) and (c), the intermittently generated pairs allow the system to simultaneously carry the magnetospherically prescribed currents and adjust the charge density and average electric field to force-free conditions. We also elucidate the conditions for pair creating beam flow to be steady (stationary with small fluctuations in the rotating frame), finding that such steady flows can occupy only a small fraction of the current density parameter space exhibited by the force-free magnetospheric model. The generic polar flow dynamics and pair creation are strongly time dependent. The model has an essential difference from almost all previous quantitative studies, in that we sought the accelerating voltage (with pair creation, when the voltage drops are sufficiently large; without, when they are small) as a function of the applied current.

X-ray Reflectivity Study of Ionic Liquids at Electrified Surfaces

NASA Astrophysics Data System (ADS)

Chu, Miaoqi

X-ray reflectivity (XRR) versatile technique that characterize the surface structures. However, due to the lack of phase information of X-ray data, the reconstruction of electron density profile (EDP) from XRR data is an ill-posed inverse problem that requires extra attention. In Chapter 1, several key concepts in XRR data analysis are reviewed. The typical XRR data acquisition procedure and methods of modeling electron density are introduced. The widely used logarithm form of merit function is justified with mathematical deduction and numerical experiment. A scheme that generates artificial reflectivity data with theoretical statistical error but not systematical error is proposed. With the methods and schemes described in Chapter 1, simulated reflectivity data of a simple one-slab model is generated and fitted to test the efficient of EDP reconstruction. By isolating the parameters, the effects of slab width, electron density contrast and maximal wave transfer are studied individually. It?s demonstrated that best-fit/global minima, result reported by most XRR studies, don?t necessary reflect the real EDP. By contrast, mapping the merit function in the parametric space can capture much more details. Additionally, the widely accepted concept about the XRR theoretical spatial resolution (pi/q_{max}) as well the using Patterson function are brought to test. In the perspective of XRR data analysis, this chapter puts forward general rules to design and optimize XRR experiments. It also demonstrates how susceptible the fitting result will be if it?s not done carefully. In Chapter 3, the interface between hydrophobic OTS film and several solvents is studied with XRR in a transmission-cell setup. The solvents, from water, acetone, to alcohol (methanol, ethanol, 1-propanol), to alkane (pentane, hexane and heptane), vary significantly in terms of polarity and hydrogen bonding. However, the XRR data from different solvents are subtle. The methods and principles elicited in previous chapters are employed to extract information about the solid-liquid interface. Electron density depletion due to methyl terminal of solvent molecules (methyl gap) and due to the reduced surface density compared to the bulk density (density gap) are analyzed. In the next Chapter, XRR technique is employed to study the structures and dynamics of room temperature ionic liquids (RTILs) at an electrified surface. RTILs are molten salts at room temperature, consisted purely by anions and cations, with potential applications in energy storage, electro-synthesis, electrodeposition etc. The solvent-free and high charge concentrated novel liquids process many unique properties that not seen in normal dilute salt solution. It is predicted that when a surface isn't highly charged, RTILs form alternating layers of anion/cation to screen the surface charge; when it's highly charged, a crowding layer with ions with like charge forms. The alternating structure has been observed experimentally but not the crowding layer. Following the rules of optimization XRR experiment in Chapter 2, conductive silicon which has small electron density is used which maximize the EDP contrast. This makes it possible to directly observe the formation of crowding layer. The thickness of this crowding layer, charge distributions and compositions as a function of applied voltage. The dynamics of anion/cation reorganization in RTILs determine the power density for RTILs? energy application. In Chapter 5, the time-dependence of the formation and dissipation of the crowding layer is studied with XRR. An ultra-slow dynamic, much longer than the typical RC time constant, is revealed. Comparisons with theoretical predications and experiments studies are made in order to understand the origin of this process. The thesis is summarized in Chapter 6, along with several proposals for future work.

Anomalous columnar order of charged colloidal platelets

NASA Astrophysics Data System (ADS)

Morales-Anda, L.; Wensink, H. H.; Galindo, A.; Gil-Villegas, A.

2012-01-01

Monte Carlo computer simulations are carried out for a model system of like-charged colloidal platelets in the isothermal-isobaric ensemble (NpT). The aim is to elucidate the role of electrostatic interactions on the structure of synthetic clay systems at high particle densities. Short-range repulsions between particles are described by a suitable hard-core model representing a discotic particle. This potential is supplemented with an electrostatic potential based on a Yukawa model for the screened Coulombic potential between infinitely thin disklike macro-ions. The particle aspect-ratio and electrostatic parameters were chosen to mimic an aqueous dispersion of thin, like-charged, rigid colloidal platelets at finite salt concentration. An examination of the fluid phase diagram reveals a marked shift in the isotropic-nematic transition compared to the hard cut-sphere reference system. Several statistical functions, such as the pair correlation function for the center-of-mass coordinates and structure factor, are obtained to characterize the structural organization of the platelets phases. At low salinity and high osmotic pressure we observe anomalous hexagonal columnar structures characterized by interpenetrating columns with a typical intercolumnar distance corresponding to about half of that of a regular columnar phase. Increasing the ionic strength leads to the formation of glassy, disordered structures consisting of compact clusters of platelets stacked into finite-sized columns. These so-called "nematic columnar" structures have been recently observed in systems of charge-stabilized gibbsite platelets. Our findings are corroborated by an analysis of the static structure factor from a simple density functional theory.

Quantum chemical density functional theory studies on the molecular structure and vibrational spectra of mannitol

NASA Astrophysics Data System (ADS)

Moorthi, P. P.; Gunasekaran, S.; Swaminathan, S.; Ramkumaar, G. R.

2015-02-01

A collective experimental and theoretical study was conducted on the molecular structure and vibrational spectra of mannitol. The FT-IR and FT-Raman spectra of mannitol were recorded in the solid phase. The molecular geometry, vibrational frequencies, thermodynamic functions and atomic charges of mannitol in the ground state have been calculated by using the ab initio HF (Hartree-Fock) and density functional methods (B3LYP) invoking cc-pVDZ basis set. The complete vibrational assignments were performed on the basis of Total Energy Distribution (TED) of the vibrational modes. The UV absorption spectra of the title compound dissolved in water. Natural bond orbital analysis has been carried out to explain the charge transfer or delocalization of charge due to the intra-molecular interactions. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO methods. The first order hyperpolarizability (β0) of this novel molecular system and related properties (β, α0 and Δα) of mannitol are calculated using B3LYP/cc-pVDZ and HF/cc-pVDZ methods on the finite-field approach. By using TD-DFT calculation, electronic absorption spectra of the title compound have been predicted and a good agreement with experimental one is established. In addition, the molecular electrostatic potential (MEP) have been investigated using theoretical calculations, the calculated HOMO and LUMO energies shows that the charge transfer within the molecule.

Tunable charge donation and spin polarization of metal adsorbates on graphene using an applied electric field

NASA Astrophysics Data System (ADS)

Parq, Jae-Hyeon; Yu, Jaejun; Kwon, Young-Kyun; Kim, Gunn

2010-11-01

Metal atoms on graphene, when ionized, can act as a point-charge impurity to probe a charge response of graphene with the Dirac cone band structure. To understand the microscopic physics of the metal-atom-induced charge and spin polarization in graphene, we present scanning tunneling spectroscopy (STS) simulations based on density-functional theory calculations. We find that a Cs atom on graphene is fully ionized with a significant band-bending feature in the STS whereas the charge and magnetic states of Ba and La atoms on graphene appear to be complicated due to orbital hybridization and Coulomb interaction. By applying external electric field, we observe changes in charge donations and spin magnetic moments of the metal adsorbates on graphene.

A Density Functional Approach to Polarizable Models: A Kim-Gordon-Response Density Interaction Potential for Molecular Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tabacchi, G; Hutter, J; Mundy, C

2005-04-07

A combined linear response--frozen electron density model has been implemented in a molecular dynamics scheme derived from an extended Lagrangian formalism. This approach is based on a partition of the electronic charge distribution into a frozen region described by Kim-Gordon theory, and a response contribution determined by the instaneous ionic configuration of the system. The method is free from empirical pair-potentials and the parameterization protocol involves only calculations on properly chosen subsystems. They apply this method to a series of alkali halides in different physical phases and are able to reproduce experimental structural and thermodynamic properties with an accuracy comparablemore » to Kohn-Sham density functional calculations.« less

Flexoelectricity in ATiO3 (A = Sr, Ba, Pb) perovskite oxide superlattices from density functional theory

NASA Astrophysics Data System (ADS)

Plymill, Austin; Xu, Haixuan

2018-04-01

Flexoelectric coefficients for several bulk and superlattice perovskite systems are determined using a direct approach from first principles density functional theory calculations. A strong enhancement in the longitudinal flexoelectric coefficient has been observed in the 1SrTiO3/1PbTiO3 superlattice with alternating single atomic layers of SrTiO3 and PbTiO3. It was found that atomistic displacement, charge response under strain, and interfaces affect the flexoelectric properties of perovskite superlattice systems. These factors can be used to tune this effect in dielectrics. It was further found that the calculated Born effective charge for an ion under the influence of strain can differ significantly from the bulk value. These insights can be used to help search for more effective flexoelectric materials to be implemented in electromechanical devices.

Probing Sizes and Shapes of Nobelium Isotopes by Laser Spectroscopy

NASA Astrophysics Data System (ADS)

Raeder, S.; Ackermann, D.; Backe, H.; Beerwerth, R.; Berengut, J. C.; Block, M.; Borschevsky, A.; Cheal, B.; Chhetri, P.; Düllmann, Ch. E.; Dzuba, V. A.; Eliav, E.; Even, J.; Ferrer, R.; Flambaum, V. V.; Fritzsche, S.; Giacoppo, F.; Götz, S.; Heßberger, F. P.; Huyse, M.; Kaldor, U.; Kaleja, O.; Khuyagbaatar, J.; Kunz, P.; Laatiaoui, M.; Lautenschläger, F.; Lauth, W.; Mistry, A. K.; Minaya Ramirez, E.; Nazarewicz, W.; Porsev, S. G.; Safronova, M. S.; Safronova, U. I.; Schuetrumpf, B.; Van Duppen, P.; Walther, T.; Wraith, C.; Yakushev, A.

2018-06-01

Until recently, ground-state nuclear moments of the heaviest nuclei could only be inferred from nuclear spectroscopy, where model assumptions are required. Laser spectroscopy in combination with modern atomic structure calculations is now able to probe these moments directly, in a comprehensive and nuclear-model-independent way. Here we report on unique access to the differential mean-square charge radii of No 252 ,253 ,254 , and therefore to changes in nuclear size and shape. State-of-the-art nuclear density functional calculations describe well the changes in nuclear charge radii in the region of the heavy actinides, indicating an appreciable central depression in the deformed proton density distribution in No,254252 isotopes. Finally, the hyperfine splitting of No 253 was evaluated, enabling a complementary measure of its (quadrupole) deformation, as well as an insight into the neutron single-particle wave function via the nuclear spin and magnetic moment.

Electronic Reconstruction at the Isopolar LaTiO3/LaFeO3 Interface: An X-Ray Photoemission and Density-Functional Theory Study

NASA Astrophysics Data System (ADS)

Kleibeuker, J. E.; Zhong, Z.; Nishikawa, H.; Gabel, J.; Müller, A.; Pfaff, F.; Sing, M.; Held, K.; Claessen, R.; Koster, G.; Rijnders, G.

2014-12-01

We report the formation of a nonmagnetic band insulator at the isopolar interface between the antiferromagnetic Mott-Hubbard insulator LaTiO3 and the antiferromagnetic charge transfer insulator LaFeO3. By density-functional theory calculations, we find that the formation of this interface state is driven by the combination of O band alignment and crystal field splitting energy of the t2 g and eg bands. As a result of these two driving forces, the Fe 3 d bands rearrange and electrons are transferred from Ti to Fe. This picture is supported by x-ray photoelectron spectroscopy, which confirms the rearrangement of the Fe 3 d bands and reveals an unprecedented charge transfer up to 1.2 ±0.2 e-/interface unit cell in our LaTiO3/LaFeO3 heterostructures.

Maximizing ion current rectification in a bipolar conical nanopore fluidic diode using optimum junction location.

PubMed

Singh, Kunwar Pal

2016-10-12

The ion current rectification has been obtained as a function of the location of a heterojunction in a bipolar conical nanopore fluidic diode for different parameters to determine the junction location for maximum ion current rectification using numerical simulations. Forward current peaks for a specific location of the junction and reverse current decreases with the junction location due to a change in ion enrichment/depletion in the pore. The optimum location of the heterojunction shifts towards the tip with base/tip diameter and surface charge density, and towards the base with the electrolyte concentration. The optimum location of the heterojunction has been approximated by an equation as a function of pore length, base/tip diameter, surface charge density and electrolyte concentration. The study is useful to design a rectifier with maximum ion current rectification for practical purposes.

Photoelectron Spectroscopy of Free Polyoxoanions Mo6O19 2- and W6O19 2- in the Gas Phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Infante, Ivan A.; Visscher, Lucas; Wang, Xue B.

2004-09-22

Two doubly charged polyoxoanions, Mo6O19 2- and W6O19 2-, were observed in the gas phase using electrospray ionization. Their electronic structures were investigated using photoelectron spectroscopy and quasi-relativistic density functional calculations. Each dianion was found to be highly stable despite the presence of strong intramolecular coulomb repulsion, estimated to be about 2 eV for each system. The valence detachment features were all shown to originate from electronic excitations involving oxygen lone-pair type orbitals. Their observed energies were in excellent agreement with the theoretical vertical detachment energies calculated using time-dependent density functional theory. Despite being multiply charged, polyoxometalate oxide clusters canmore » be studied in the gas phase, providing the opportunity for detailed benchmark theoretical studies on the electronic structures of these important transition-metal oxide systems.« less

Multistage electronic nematic transitions in cuprate superconductors: A functional-renormalization-group analysis

NASA Astrophysics Data System (ADS)

Tsuchiizu, Masahisa; Kawaguchi, Kouki; Yamakawa, Youichi; Kontani, Hiroshi

2018-04-01

Recently, complex rotational symmetry-breaking phenomena have been discovered experimentally in cuprate superconductors. To find the realized order parameters, we study various unconventional charge susceptibilities in an unbiased way by applying the functional-renormalization-group method to the d -p Hubbard model. Without assuming the wave vector of the order parameter, we reveal that the most dominant instability is the uniform (q =0 ) charge modulation on the px and py orbitals, which possesses d symmetry. This uniform nematic order triggers another nematic p -orbital density wave along the axial (Cu-Cu) direction at Qa≈(π /2 ,0 ) . It is predicted that uniform nematic order is driven by the spin fluctuations in the pseudogap region, and another nematic density-wave order at q =Qa is triggered by the uniform order. The predicted multistage nematic transitions are caused by Aslamazov-Larkin-type fluctuation-exchange processes.

Dielectric and vibrational properties of amino acids

NASA Astrophysics Data System (ADS)

Tulip, P. R.; Clark, S. J.

2004-09-01

We calculate polarizability tensors and normal mode frequencies for the amino acids alanine, leucine, isoleucine, and valine using density functional perturbation theory implemented within the plane wave pseudopotential framework. It is found that the behavior of the electron density under external fields depends to a large extent on the geometrical structure of the molecule in question, rather than simply on the constituent functional groups. The normal modes are able to help distinguish between the different types of intramolecular hydrogen bonding present, and help to explain why leucine is found in the zwitterionic form for the gaseous phase. Calculated IR spectra show a marked difference between those obtained for zwitterionic and nonzwitterionic molecules. These differences can be attributed to the different chemical and hydrogen bonds present. Effective dynamical charges are calculated, and compared to atomic charges obtained from Mulliken population analysis. It is found that disagreement exists, largely due to the differing origins of these quantities.

Different electronic and charge-transport properties of four organic semiconductors Tetraazaperopyrenes derivatives

NASA Astrophysics Data System (ADS)

Shi, Yarui; Wei, Huiling; Liu, Yufang

2015-03-01

Tetraazaperopyrenes (TAPPs) derivatives are high-performance n-type organic semiconductor material families with the remarkable long-term stabilities. The charge carrier mobilities in TAPPs derivatives crystals were calculated by the density functional theory (DFT) method combined with the Marcus-Hush electron-transfer theory. The existence of considerable C-H…F-C bonding defines the conformation of the molecular structure and contributes to its stability. We illustrated how it is possible to control the electronic and charge-transport parameters of TAPPs derivatives as a function of the positions, a type of the substituents. It is found that the core substitution of TAPPs has a drastic influence on the charge-transport mobilities. The maximum electron mobility value of the core-brominated 2,9-bis (perfluoroalkyl)-substituted TAPPs is 0.521 cm2 V-1 s-1, which appear in the orientation angle 95° and 275°. The results demonstrate that the TAPPs with bromine substituents in ortho positions exhibit the best charge-transfer efficiency among the four different TAPP derivatives.

Density functional theory and an experimentally-designed energy functional of electron density.

PubMed

Miranda, David A; Bueno, Paulo R

2016-09-21

We herein demonstrate that capacitance spectroscopy (CS) experimentally allows access to the energy associated with the quantum mechanical ground state of many-electron systems. Priorly, electrochemical capacitance, C [small mu, Greek, macron] [ρ], was previously understood from conceptual and computational density functional theory (DFT) calculations. Thus, we herein propose a quantum mechanical experiment-based variational method for electron charging processes based on an experimentally-designed functional of the ground state electron density. In this methodology, the electron state density, ρ, and an energy functional of the electron density, E [small mu, Greek, macron] [ρ], can be obtained from CS data. CS allows the derivative of the electrochemical potential with respect to the electron density, (δ[small mu, Greek, macron][ρ]/δρ), to be obtained as a unique functional of the energetically minimised system, i.e., β/C [small mu, Greek, macron] [ρ], where β is a constant (associated with the size of the system) and C [small mu, Greek, macron] [ρ] is an experimentally observable quantity. Thus the ground state energy (at a given fixed external potential) can be obtained simply as E [small mu, Greek, macron] [ρ], from the experimental measurement of C [small mu, Greek, macron] [ρ]. An experimental data-set was interpreted to demonstrate the potential of this quantum mechanical experiment-based variational principle.

Transport model of controlled molecular rectifier showing unusual negative differential resistance effect.

PubMed

Granhen, Ewerton Ramos; Reis, Marcos Allan Leite; Souza, Fabrício M; Del Nero, Jordan

2010-12-01

We investigate theoretically the charge accumulated Q in a three-terminal molecular device in the presence of an external electric field. Our approach is based on ab initio Hartree-Fock and density functional theory methodology contained in Gaussian package. Our main finding is a negative differential resistance (NDR) in the charge Q as a function of an external electric field. To explain this NDR effect we apply a phenomenological capacitive model based on a quite general system composed of many localized levels (that can be LUMOs of a molecule) coupled to source and drain. The capacitance accounts for charging effects that can result in Coulomb blockade (CB) in the transport. We show that this CB effect gives rise to a NDR for a suitable set of phenomenological parameters, like tunneling rates and charging energies. The NDR profile obtained in both ab initio and phenomenological methodologies are in close agreement.

Semiclassics, Goldstone bosons and CFT data

NASA Astrophysics Data System (ADS)

Monin, A.; Pirtskhalava, D.; Rattazzi, R.; Seibold, F. K.

2017-06-01

Hellerman et al. (arXiv:1505.01537) have shown that in a generic CFT the spectrum of operators carrying a large U(1) charge can be analyzed semiclassically in an expansion in inverse powers of the charge. The key is the operator state correspondence by which such operators are associated with a finite density superfluid phase for the theory quantized on the cylinder. The dynamics is dominated by the corresponding Goldstone hydrodynamic mode and the derivative expansion coincides with the inverse charge expansion. We illustrate and further clarify this situation by first considering simple quantum mechanical analogues. We then systematize the approach by employing the coset construction for non-linearly realized space-time symmetries. Focussing on CFT3 we illustrate the case of higher rank and non-abelian groups and the computation of higher point functions. Three point function coefficients turn out to satisfy universal scaling laws and correlations as the charge and spin are varied.

Charging and geometric effects on conduction through Anthracene molecular junctions

NASA Astrophysics Data System (ADS)

Kaur, Rupan Preet; Sawhney, Ravinder Singh; Engles, Derick

We studied the geometric effects on the charge transfer through the anthracenedithiol (ADT) molecular junction using density functional theory combined with the non-equilibrium Green’s function approach. Two major geometric aspects, bond length and bond angle, were moderated to optimize the electrical conduction. From the results established in this paper, we found that the electrical conduction can be tuned from 0.2 G0 to 0.9 G0 by varying the Au-S bond length, whereas the moderation of bonding angle assayed a minor change from 0.37 G0 to 0.47 G0. We attributed this escalating zero bias conductance to the increasing charge on the terminal sulfur atom of the ADT molecule, which increased the energy of the HOMO orbital towards Fermi level and exhibited a semi-metallic behaviour. Therefore, geometry plays a critical role in deciding the charge transport through the metal/molecule interface.

Self-consistent pseudopotential calculation of the bulk properties of Mo and W

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zunger, A.; Cohen, M.L.

The bulk properties of Mo and W are calculated using the recently developed momentum-space approach for calculating total energy via a nonlocal pseudopotential. This approach avoids any shape approximation to the variational charge density (e.g., muffin tins), is fully self-consistent, and replaces the multidimensional and multicenter integrals akin to real-space representations by simple and readily convergent reciprocal-space lattice sums. We use first-principles atomic pseudopotentials which have been previously demonstrated to yield band structures and charge densities for both semiconductors and transition metals in good agreement with experiment and all-electron calculations. Using a mixed-basis representation for the crystalline wave function, wemore » are able to accurately reproduce both the localized and itinerant features of the electronic states in these systems. These first-principles pseudopotentials, together with the self-consistent density-functional representation for both the exchange and the correlation screening, yields agreement with experiment of 0.2% in the lattice parameters, 2% and 11% for the binding energies of Mo and W, respectively, and 12% and 7% for the bulk moduli of Mo and W, respectively.« less

DNA Nucleotides Detection via capacitance properties of Graphene

NASA Astrophysics Data System (ADS)

Khadempar, Nahid; Berahman, Masoud; Yazdanpanah, Arash

2016-05-01

In the present paper a new method is suggested to detect the DNA nucleotides on a first-principles calculation of the electronic features of DNA bases which chemisorbed to a graphene sheet placed between two gold electrodes in a contact-channel-contact system. The capacitance properties of graphene in the channel are surveyed using non-equilibrium Green's function coupled with the Density Functional Theory. Thus, the capacitance properties of graphene are theoretically investigated in a biological environment, and, using a novel method, the effect of the chemisorbed DNA nucleotides on electrical charges on the surface of graphene is deciphered. Several parameters in this method are also extracted including Electrostatic energy, Induced density, induced electrostatic potential, Electron difference potential and Electron difference density. The qualitative and quantitative differences among these parameters can be used to identify DNA nucleotides. Some of the advantages of this approach include its ease and high accuracy. What distinguishes the current research is that it is the first experiment to investigate the capacitance properties of gaphene changes in the biological environment and the effect of chemisorbed DNA nucleotides on the surface of graphene on the charge.

Scaling of charged particle production in d+Au collisions at √(sNN)=200GeV

NASA Astrophysics Data System (ADS)

Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Becker, B.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Busza, W.; Carroll, A.; Decowski, M. P.; García, E.; Gburek, T.; George, N.; Gulbrandsen, K.; Gushue, S.; Halliwell, C.; Hamblen, J.; Harrington, A. S.; Henderson, C.; Hofman, D. J.; Hollis, R. S.; Hołyński, R.; Holzman, B.; Iordanova, A.; Johnson, E.; Kane, J. L.; Khan, N.; Kulinich, P.; Kuo, C. M.; Lee, J. W.; Lin, W. T.; Manly, S.; Mignerey, A. C.; Nouicer, R.; Olszewski, A.; Pak, R.; Park, I. C.; Pernegger, H.; Reed, C.; Roland, C.; Roland, G.; Sagerer, J.; Sarin, P.; Sedykh, I.; Skulski, W.; Smith, C. E.; Steinberg, P.; Stephans, G. S.; Sukhanov, A.; Tonjes, M. B.; Trzupek, A.; Vale, C.; Nieuwenhuizen, G. J.; Verdier, R.; Veres, G. I.; Wolfs, F. L.; Wosiek, B.; Woźniak, K.; Wysłouch, B.; Zhang, J.

2005-09-01

The measured pseudorapidity distributions of primary charged particles over a wide pseudorapidity range of |η|≤5.4 and integrated charged particle multiplicities in d+Au collisions at √(sNN)=200GeV are presented as a function of collision centrality. The longitudinal features of d+Au collisions at √(sNN)=200GeV are found to be very similar to those seen in p+A collisions at lower energies. The total multiplicity of charged particles is found to scale with the total number of participants according to NdAuch=1/2Nppch, and the energy dependence of the density of charged particles produced in the fragmentation region exhibits extended longitudinal scaling.

Accuracy of ab initio electron correlation and electron densities in vanadium dioxide

DOE PAGES

Kylänpää, Ilkka; Balachandran, Janakiraman; Ganesh, Panchapakesan; ...

2017-11-27

Here, diffusion quantum Monte Carlo results are used as a reference to analyze properties related to phase stability and magnetism in vanadium dioxide computed with various formulations of density functional theory. We introduce metrics related to energetics, electron densities and spin densities that give us insight on both local and global variations in the antiferromagnetic M1 and R phases. Importantly, these metrics can address contributions arising from the challenging description of the 3d orbital physics in this material. We observe that the best description of energetics between the structural phases does not correspond to the best accuracy in the charge density, which is consistent with observations made recently by Medvedev et~al. in the context of isolated atoms. However, we do find evidence that an accurate spin density connects to correct energetic ordering of different magnetic states in VOmore » $$_2$$, although local, semilocal, and meta-GGA functionals tend to erroneously favor demagnetization of the vanadium sites. The recently developed SCAN functional stands out as remaining nearly balanced in terms of magnetization across the M1-R transition and correctly predicting the ground state crystal structure. In addition to ranking current density functionals, our reference energies and densities serve as important benchmarks for future functional development.« less

Time-dependent density-functional tight-binding method with the third-order expansion of electron density

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishimoto, Yoshio, E-mail: nishimoto.yoshio@fukui.kyoto-u.ac.jp

2015-09-07

We develop a formalism for the calculation of excitation energies and excited state gradients for the self-consistent-charge density-functional tight-binding method with the third-order contributions of a Taylor series of the density functional theory energy with respect to the fluctuation of electron density (time-dependent density-functional tight-binding (TD-DFTB3)). The formulation of the excitation energy is based on the existing time-dependent density functional theory and the older TD-DFTB2 formulae. The analytical gradient is computed by solving Z-vector equations, and it requires one to calculate the third-order derivative of the total energy with respect to density matrix elements due to the inclusion of themore » third-order contributions. The comparison of adiabatic excitation energies for selected small and medium-size molecules using the TD-DFTB2 and TD-DFTB3 methods shows that the inclusion of the third-order contributions does not affect excitation energies significantly. A different set of parameters, which are optimized for DFTB3, slightly improves the prediction of adiabatic excitation energies statistically. The application of TD-DFTB for the prediction of absorption and fluorescence energies of cresyl violet demonstrates that TD-DFTB3 reproduced the experimental fluorescence energy quite well.« less

Time-dependent density-functional tight-binding method with the third-order expansion of electron density.

PubMed

Nishimoto, Yoshio

2015-09-07

We develop a formalism for the calculation of excitation energies and excited state gradients for the self-consistent-charge density-functional tight-binding method with the third-order contributions of a Taylor series of the density functional theory energy with respect to the fluctuation of electron density (time-dependent density-functional tight-binding (TD-DFTB3)). The formulation of the excitation energy is based on the existing time-dependent density functional theory and the older TD-DFTB2 formulae. The analytical gradient is computed by solving Z-vector equations, and it requires one to calculate the third-order derivative of the total energy with respect to density matrix elements due to the inclusion of the third-order contributions. The comparison of adiabatic excitation energies for selected small and medium-size molecules using the TD-DFTB2 and TD-DFTB3 methods shows that the inclusion of the third-order contributions does not affect excitation energies significantly. A different set of parameters, which are optimized for DFTB3, slightly improves the prediction of adiabatic excitation energies statistically. The application of TD-DFTB for the prediction of absorption and fluorescence energies of cresyl violet demonstrates that TD-DFTB3 reproduced the experimental fluorescence energy quite well.

Accuracy of ab initio electron correlation and electron densities in vanadium dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kylänpää, Ilkka; Balachandran, Janakiraman; Ganesh, Panchapakesan

Here, diffusion quantum Monte Carlo results are used as a reference to analyze properties related to phase stability and magnetism in vanadium dioxide computed with various formulations of density functional theory. We introduce metrics related to energetics, electron densities and spin densities that give us insight on both local and global variations in the antiferromagnetic M1 and R phases. Importantly, these metrics can address contributions arising from the challenging description of the 3d orbital physics in this material. We observe that the best description of energetics between the structural phases does not correspond to the best accuracy in the charge density, which is consistent with observations made recently by Medvedev et~al. in the context of isolated atoms. However, we do find evidence that an accurate spin density connects to correct energetic ordering of different magnetic states in VOmore » $$_2$$, although local, semilocal, and meta-GGA functionals tend to erroneously favor demagnetization of the vanadium sites. The recently developed SCAN functional stands out as remaining nearly balanced in terms of magnetization across the M1-R transition and correctly predicting the ground state crystal structure. In addition to ranking current density functionals, our reference energies and densities serve as important benchmarks for future functional development.« less

The Structures of Fibronectin Adsorbed on Polyelectrolyte Thin Films

NASA Astrophysics Data System (ADS)

Shin, Kwanwoo; Satija, Sushil; Fang, Xiao-Hua; Li, Bin-Quan; Nadine, Pernodet; Miriam, Rafailovich; Sokolov, Jonathan; Arach, Goldar; Roser, Steve

2002-03-01

We have shown that it is possible to form a fibrilar network of fibronectin on a polyelectrolyte polymer film whose dimensions are similar to those reported on the extra cellular matrix. The fibronectin network was observed to form only when the charge density of the polymer was in excess of the natural charge density of the cell wall. Furthermore, the self-organized fibronectin layer was much thicker than the polymer film, indicating that long ranged interaction may play a key role in the assembly process. It is therefore important to understand the structure of the polymer layer/protein interface. Here we report on a neutron reflectivity study where we explore the structure of the polyelectrolyte layer, in this case sulfonated polystyrene (PSS_x.), with varying degree of sulfonation (x<30%), as a function of sulfur content and counter ion concentration. These results are then correlated with systemic study of the adsorption and the multilayer formation of fibronectin as a function of incubation time for various sulfonation levels of PSS_x. Furthermore, the surface charge on the substrates can be strongly influenced by the presence of salt ions, it is important to understand changes due to electrostatic interactions occurring in the various salt conditions. Complementary X-ray reflection was used to determine the salt density profile associating with the internal ionic polymer matrix. This work was funded in part of the NSF-MRSEC program.

Possible impact of multi-electron loss events on the average beam charge state in an HIF target chamber and a neutral beam approach

NASA Astrophysics Data System (ADS)

Grisham, L. R.

2001-05-01

Experiments were carried out during the early 1980s to assess the obtainable atomic neutralization of energetic beams of negative ions ranging from lithium to silicon. The experiments found (Grisham et al. Rev. Sci. Instrum. 53 (1982) 281; Princeton Plasma Physics Laboratory Report PPPL-1857, 1981) that, for higher atomic number elements than lithium, it appeared that a substantial fraction of the time more than one electron was being lost in a single collision. This result was inferred from the existence of more than one ionization state in the product beam for even the thinnest line densities at which any electron removal took place. Because of accelerator limitations, these experiments were limited to maximum energies of 7 MeV. However, based upon these results, it is possible that multi-electron loss events may also play a significant role in determining the average ion charge state of the much higher Z and more energetic beams traversing the medium in an heavy ion fusion chamber. This could result in the beam charge state being considerably higher than previously anticipated, and might require designers to consider harder vacuum ballistic focusing approaches, or the development of additional space charge neutralization schemes. This paper discusses the measurements that gave rise for these concerns, as well as a description of further measurements that are proposed to be carried out for atomic numbers and energies per amu which would be closer to those required for heavy ion fusion drivers. With a very low current beam of a massive, but low charge state energetic ion, the charge state distribution emerging from a target gas cell could be measured as a function of line density and medium composition. Varying the line density would allow one to simulate the charge state evolution of the beam as a function of distance into the target chamber. This paper also briefly discusses a possible alternative driver approach using photodetachment-neutralized atomic beams, which could reduce plasma complications far from the target, but which would impose more stringent limitations upon chamber pressure and repetition rate.

Magnetic-Field Density-Functional Theory (BDFT): Lessons from the Adiabatic Connection.

PubMed

Reimann, Sarah; Borgoo, Alex; Tellgren, Erik I; Teale, Andrew M; Helgaker, Trygve

2017-09-12

We study the effects of magnetic fields in the context of magnetic field density-functional theory (BDFT), where the energy is a functional of the electron density ρ and the magnetic field B. We show that this approach is a worthwhile alternative to current-density functional theory (CDFT) and may provide a viable route to the study of many magnetic phenomena using density-functional theory (DFT). The relationship between BDFT and CDFT is developed and clarified within the framework of the four-way correspondence of saddle functions and their convex and concave parents in convex analysis. By decomposing the energy into its Kohn-Sham components, we demonstrate that the magnetizability is mainly determined by those energy components that are related to the density. For existing density functional approximations, this implies that, for the magnetizability, improvements of the density will be more beneficial than introducing a magnetic-field dependence in the correlation functional. However, once a good charge density is achieved, we show that high accuracy is likely only obtainable by including magnetic-field dependence. We demonstrate that adiabatic-connection (AC) curves at different field strengths resemble one another closely provided each curve is calculated at the equilibrium geometry of that field strength. In contrast, if all AC curves are calculated at the equilibrium geometry of the field-free system, then the curves change strongly with increasing field strength due to the increasing importance of static correlation. This holds also for density functional approximations, for which we demonstrate that the main error encountered in the presence of a field is already present at zero field strength, indicating that density-functional approximations may be applied to systems in strong fields, without the need to treat additional static correlation.

Origin of the different transport properties of electron and hole polarons in an ambipolar polyselenophene-based conjugated polymer

NASA Astrophysics Data System (ADS)

Chen, Zhuoying; Bird, Matthew; Lemaur, Vincent; Radtke, Guillaume; Cornil, Jérôme; Heeney, Martin; McCulloch, Iain; Sirringhaus, Henning

2011-09-01

Understanding the mechanisms limiting ambipolar transport in conjugated polymer field-effect transistors (FETs) is of both fundamental and practical interest. Here, we present a systematic study comparing hole and electron charge transport in an ambipolar conjugated polymer, semicrystalline poly(3,3''-di-n-decylterselenophene) (PSSS). Starting from a detailed analysis of the device characteristics and temperature/charge-density dependence of the mobility, we interpret the difference between hole and electron transport through both the Vissenberg-Matters and the mobility-edge model. To obtain microscopic insight into the quantum mechanical wave function of the charges at a molecular level, we combine charge modulation spectroscopy (CMS) measuring the charge-induced absorption signatures from positive and negative polarons in these ambipolar FETs with corresponding density functional theory (DFT) calculations. We observe a significantly higher switch-on voltage for electrons than for holes due to deep electron trap states, but also a higher activation energy of the mobility for mobile electrons. The CMS spectra reveal that the electrons that remain mobile and contribute to the FET current have a wave function that is more localized onto a single polymer chain than that of holes, which is extended over several polymer chains. We interpret this as evidence that the transport properties of the mobile electrons in PSSS are still affected by the presence of deep electron traps. The more localized electron state could be due to the mobile electrons interacting with shallow trap states in the vicinity of a chemical, potentially water-related, impurity that might precede the capture of the electron into a deeply trapped state.

Scanning gate microscopy of quantum rings: effects of an external magnetic field and of charged defects.

PubMed

Pala, M G; Baltazar, S; Martins, F; Hackens, B; Sellier, H; Ouisse, T; Bayot, V; Huant, S

2009-07-01

We study scanning gate microscopy (SGM) in open quantum rings obtained from buried semiconductor InGaAs/InAlAs heterostructures. By performing a theoretical analysis based on the Keldysh-Green function approach we interpret the radial fringes observed in experiments as the effect of randomly distributed charged defects. We associate SGM conductance images with the local density of states (LDOS) of the system. We show that such an association cannot be made with the current density distribution. By varying an external magnetic field we are able to reproduce recursive quasi-classical orbits in LDOS and conductance images, which bear the same periodicity as the Aharonov-Bohm effect.

Nonperturbative vacuum polarization effects in two-dimensional supercritical Dirac-Coulomb system I. Vacuum charge density

NASA Astrophysics Data System (ADS)

Davydov, A.; Sveshnikov, K.; Voronina, Yu.

2018-01-01

Based on the original combination of analytical methods, computer algebra tools and numerical calculations, proposed recently in Refs. 1-3, the nonperturbative vacuum polarization effects in the 2+1D supercritical Dirac-Coulomb system with Z > Zcr,1 are explored. Both the vacuum charge density ρV P(r→) and vacuum energy ℰV P are considered. The main result of the work is that in the overcritical region ℰV P turns out to be a rapidly decreasing function ˜-ηeffZ3/R with ηeff > 0 and R being the size of the external Coulomb source. Due to a lot of details of calculation the whole work is divided into two parts I and II. In the present part I, we consider the evaluation and behavior of the vacuum density ρV P, which further is used in part II for evaluation of the vacuum energy, with emphasis on the renormalization, convergence of the partial expansion for ρV P and behavior of the integral induced charge QV P in the overcritical region.

DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid

NASA Astrophysics Data System (ADS)

Renuga Devi, T. S.; Sharmi kumar, J.; Ramkumaar, G. R.

2015-02-01

The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm-1 and 4000-50 cm-1 respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee-Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic charges were calculated using both Hartee-Fock and density functional method using the cc-pVDZ basis set and compared. The calculated HOMO-LUMO energy gap revealed that charge transfer occurs within the molecule. 1H and 13C NMR chemical shifts of the molecule were calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The first order hyperpolarizability (β) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule.

The role of charge transfer in the energy level alignment at the pentacene/C60 interface.

PubMed

Beltrán, J; Flores, F; Ortega, J

2014-03-07

Understanding the mechanism of energy level alignment at organic-organic interfaces is a crucial line of research to optimize applications in organic electronics. We address this problem for the C60-pentacene interface by performing local-orbital Density Functional Theory (DFT) calculations, including the effect of the charging energies on the energy gap of both organic materials. The results are analyzed within the induced density of interface states (IDIS) model. We find that the induced interface potential is in the range of 0.06-0.10 eV, in good agreement with the experimental evidence, and that such potential is mainly induced by the small, but non-negligible, charge transfer between the two compounds and the multipolar contribution associated with pentacene. We also suggest that an appropriate external intercompound potential could create an insulator-metal transition at the interface.

Quantum many-body intermetallics: Phase stability of Fe3Al and small-gap formation in Fe2VAl

NASA Astrophysics Data System (ADS)

Kristanovski, Oleg; Richter, Raphael; Krivenko, Igor; Lichtenstein, Alexander I.; Lechermann, Frank

2017-01-01

Various intermetallic compounds harbor subtle electronic correlation effects. To elucidate this fact for the Fe-Al system, we perform a realistic many-body investigation based on a combination of density functional theory with dynamical mean-field theory in a charge self-consistent manner. A better characterization and understanding of the phase stability of bcc-based D 03-Fe3Al through an improved description of the correlated charge density and the magnetic energy is achieved. Upon replacement of one Fe sublattice with V, the Heusler compound Fe2VAl is realized, known to display bad-metal behavior and increased specific heat. Here we document a charge-gap opening at low temperatures in line with previous experimental work. The gap structure does not match conventional band theory and is reminiscent of (pseudo)gap characteristics in correlated oxides.

Dusty Plasmas in Planetary Magnetospheres Award

NASA Technical Reports Server (NTRS)

Horanyi, Mihaly

2005-01-01

This is my final report for the grant Dusty Plasmas in Planetary Magnetospheres. The funding from this grant supported our research on dusty plasmas to study: a) dust plasma interactions in general plasma environments, and b) dusty plasma processes in planetary magnetospheres (Earth, Jupiter and Saturn). We have developed a general purpose transport code in order to follow the spatial and temporal evolution of dust density distributions in magnetized plasma environments. The code allows the central body to be represented by a multipole expansion of its gravitational and magnetic fields. The density and the temperature of the possibly many-component plasma environment can be pre-defined as a function of coordinates and, if necessary, the time as well. The code simultaneously integrates the equations of motion with the equations describing the charging processes. The charging currents are dependent not only on the instantaneous plasma parameters but on the velocity, as well as on the previous charging history of the dust grains.

Ion transport in a pH-regulated nanopore.

PubMed

Yeh, Li-Hsien; Zhang, Mingkan; Qian, Shizhi

2013-08-06

Fundamental understanding of ion transport phenomena in nanopores is crucial for designing the next-generation nanofluidic devices. Due to surface reactions of dissociable functional groups on the nanopore wall, the surface charge density highly depends upon the proton concentration on the nanopore wall, which in turn affects the electrokinetic transport of ions, fluid, and particles within the nanopore. Electrokinetic ion transport in a pH-regulated nanopore, taking into account both multiple ionic species and charge regulation on the nanopore wall, is theoretically investigated for the first time. The model is verified by the experimental data of nanopore conductance available in the literature. The results demonstrate that the spatial distribution of the surface charge density at the nanopore wall and the resulting ion transport phenomena, such as ion concentration polarization (ICP), ion selectivity, and conductance, are significantly affected by the background solution properties, such as the pH and salt concentration.

Impurity Effects on Charging Mechanism and Energy Storage of Nanoporous Supercapacitors

DOE PAGES

Lian, Cheng; Liu, Kun; Liu, Honglai; ...

2017-06-08

Room-temperature ionic liquids (RTILs) have been widely used as electrolytes to enhance the capacitive performance of electrochemical capacitors also known as supercapacitors. Whereas impurities are ubiquitous in RTILs (e.g., water, alkali salts, and organic solvents), little is known about their influences on the electrochemical behavior of electrochemical devices. In this work, we investigate different impurities in RTILs within the micropores of carbon electrodes via the classical density functional theory (CDFT). We find that under certain conditions impurities can significantly change the charging behavior of electric double layers and the shape of differential capacitance curves even at very low concentrations. Moremore » interestingly, an impurity with a strong affinity to the nanopore can increase the energy density beyond a critical charging potential. As a result, our theoretical predictions provide further understanding of how impurity in RTILs affects the performance of supercapacitors.« less

Dimensional crossover of the charge density wave transition in thin exfoliated VSe2

NASA Astrophysics Data System (ADS)

Pásztor, Árpád; Scarfato, Alessandro; Barreteau, Céline; Giannini, Enrico; Renner, Christoph

2017-12-01

Isolating single unit-cell thin layers from the bulk matrix of layered compounds offers tremendous opportunities to design novel functional electronic materials. However, a comprehensive thickness dependence study is paramount to harness the electronic properties of such atomic foils and their stacking into synthetic heterostructures. Here we show that a dimensional crossover and quantum confinement with reducing thickness result in a striking non-monotonic evolution of the charge density wave transition temperature in VSe2. Our conclusion is drawn from a direct derivation of the local order parameter and transition temperature from the real space charge modulation amplitude imaged by scanning tunnelling microscopy. This study lifts the disagreement of previous independent transport measurements. We find that thickness can be a non-trivial tuning parameter and demonstrate the importance of considering a finite thickness range to accurately characterize its influence.

Tuning charge transfer in the LaTiO3/RO/LaNiO3 (R = rare-earth) superlattices by the rare-earth oxides interfaces from a first-principles calculation

NASA Astrophysics Data System (ADS)

Yao, Fen; Zhang, Lifang; Meng, Junling; Liu, Xiaojuan; Zhang, Xiong; Zhang, Wenwen; Meng, Jian; Zhang, Hongjie

2018-03-01

We investigate the internal charge transfer at the isopolar interfaces in LaTiO3/RO/LaNiO3 (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) superlattices by means of density functional theory calculations. The charge transfer from Ti sites to Ni sites in all superlattices is induced by the electronegativity difference between the elements Ti and Ni, and the lanthanide oxides interfaces can modulate the amount of charge transfer. Comparison of the perovskite heterostructures with the different rare-earth interfaces shows that increasing the deviations of bond angles from 180.0° and the oxygen motions near the interfaces enhance charge transfer. The 4f electrons themselves of rare-earth elements have faint influences on charge transfer. In addition, the reasons why our calculated 4f states of Sm and Tm elements disagree with the experimental systems have been provided. It is hoped that all the calculated results could be used to design new functional nanoelectronic devices in perovskite oxides.

Counter-ions at single charged wall: Sum rules.

PubMed

Samaj, Ladislav

2013-09-01

For inhomogeneous classical Coulomb fluids in thermal equilibrium, like the jellium or the two-component Coulomb gas, there exists a variety of exact sum rules which relate the particle one-body and two-body densities. The necessary condition for these sum rules is that the Coulomb fluid possesses good screening properties, i.e. the particle correlation functions or the averaged charge inhomogeneity, say close to a wall, exhibit a short-range (usually exponential) decay. In this work, we study equilibrium statistical mechanics of an electric double layer with counter-ions only, i.e. a globally neutral system of equally charged point-like particles in the vicinity of a plain hard wall carrying a fixed uniform surface charge density of opposite sign. At large distances from the wall, the one-body and two-body counter-ion densities go to zero slowly according to the inverse-power law. In spite of the absence of screening, all known sum rules are shown to hold for two exactly solvable cases of the present system: in the weak-coupling Poisson-Boltzmann limit (in any spatial dimension larger than one) and at a special free-fermion coupling constant in two dimensions. This fact indicates an extended validity of the sum rules and provides a consistency check for reasonable theoretical approaches.

Dispersive charge density wave excitations in Bi 2Sr 2CaCu 2O 8+δ [Dispersive charge density wave excitations and temperature dependent commensuration in Bi 2Sr 2CaCu 2O 8+δ

DOE PAGES

Chaix, L.; Ghiringhelli, G.; Peng, Y. Y.; ...

2017-06-12

Experimental evidence on high-T c cuprates reveals ubiquitous charge density wave (CDW) modulations, which coexist with superconductivity. Although the CDW had been predicted by theory, important questions remain about the extent to which the CDW influences lattice and charge degrees of freedom and its characteristics as functions of doping and temperature. These questions are intimately connected to the origin of the CDW and its relation to the mysterious cuprate pseudogap. We use ultrahigh-resolution resonant inelastic X-ray scattering to reveal new CDW character in underdoped Bi 2.2Sr 1.8Ca 0.8Dy 0.2Cu 2O 8+δ. At low temperature, we observe dispersive excitations from anmore » incommensurate CDW that induces anomalously enhanced phonon intensity, unseen using other techniques. Furthermore, near the pseudogap temperature T*, the CDW persists, but the associated excitations significantly weaken with an indication of CDW wavevector shift. The dispersive CDW excitations, phonon anomaly, and analysis of the CDW wavevector provide a comprehensive momentum-space picture of complex CDW behaviour and point to a closer relationship with the pseudogap state.« less

Development and Application of a Wireless Sensor for Space Charge Density Measurement in an Ultra-High-Voltage, Direct-Current Environment

PubMed Central

Xin, Encheng; Ju, Yong; Yuan, Haiwen

2016-01-01

A space charge density wireless measurement system based on the idea of distributed measurement is proposed for collecting and monitoring the space charge density in an ultra-high-voltage direct-current (UHVDC) environment. The proposed system architecture is composed of a number of wireless nodes connected with space charge density sensors and a base station. The space charge density sensor based on atmospheric ion counter method is elaborated and developed, and the ARM microprocessor and Zigbee radio frequency module are applied. The wireless network communication quality and the relationship between energy consumption and transmission distance in the complicated electromagnetic environment is tested. Based on the experimental results, the proposed measurement system demonstrates that it can adapt to the complex electromagnetic environment under the UHVDC transmission lines and can accurately measure the space charge density. PMID:27775627

Development and Application of a Wireless Sensor for Space Charge Density Measurement in an Ultra-High-Voltage, Direct-Current Environment.

PubMed

Xin, Encheng; Ju, Yong; Yuan, Haiwen

2016-10-20

A space charge density wireless measurement system based on the idea of distributed measurement is proposed for collecting and monitoring the space charge density in an ultra-high-voltage direct-current (UHVDC) environment. The proposed system architecture is composed of a number of wireless nodes connected with space charge density sensors and a base station. The space charge density sensor based on atmospheric ion counter method is elaborated and developed, and the ARM microprocessor and Zigbee radio frequency module are applied. The wireless network communication quality and the relationship between energy consumption and transmission distance in the complicated electromagnetic environment is tested. Based on the experimental results, the proposed measurement system demonstrates that it can adapt to the complex electromagnetic environment under the UHVDC transmission lines and can accurately measure the space charge density.

Simulation of Space Charge Dynamic in Polyethylene Under DC Continuous Electrical Stress

NASA Astrophysics Data System (ADS)

Boukhari, Hamed; Rogti, Fatiha

2016-10-01

The space charge dynamic plays a very important role in the aging and breakdown of polymeric insulation materials under high voltage. This is due to the intensification of the local electric field and the attendant chemical-mechanical effects in the vicinity around the trapped charge. In this paper, we have investigated the space charge dynamic in low-density polyethylene under high direct-current voltage, which is evaluated by experimental conditions. The evaluation is on the basis of simulation using a bipolar charge transport model consisting of charge injection, transports, trapping, detrapping, and recombination phenomena. The theoretical formulation of the physical problem is based on the Poisson, the continuity, and the transport equations. Numerical results provide temporal and local distributions of the electric field, the space charge density for the different kinds of charges (net charge density, mobile and trapped of electron density, mobile hole density), conduction and displacement current densities, and the external current. The result shows the appearance of the negative packet-like space charge with a large amount of the bulk under the dc electric field of 100 kV/mm, and the induced distortion of the electric field is largely near to the anode, about 39% higher than the initial electric field applied.

Benchmarking density functional theory predictions of framework structures and properties in a chemically diverse test set of metal-organic frameworks

DOE PAGES

Nazarian, Dalar; Ganesh, P.; Sholl, David S.

2015-09-30

We compiled a test set of chemically and topologically diverse Metal–Organic Frameworks (MOFs) with high accuracy experimentally derived crystallographic structure data. The test set was used to benchmark the performance of Density Functional Theory (DFT) functionals (M06L, PBE, PW91, PBE-D2, PBE-D3, and vdW-DF2) for predicting lattice parameters, unit cell volume, bonded parameters and pore descriptors. On average PBE-D2, PBE-D3, and vdW-DF2 predict more accurate structures, but all functionals predicted pore diameters within 0.5 Å of the experimental diameter for every MOF in the test set. The test set was also used to assess the variance in performance of DFT functionalsmore » for elastic properties and atomic partial charges. The DFT predicted elastic properties such as minimum shear modulus and Young's modulus can differ by an average of 3 and 9 GPa for rigid MOFs such as those in the test set. Moreover, we calculated the partial charges by vdW-DF2 deviate the most from other functionals while there is no significant difference between the partial charges calculated by M06L, PBE, PW91, PBE-D2 and PBE-D3 for the MOFs in the test set. We find that while there are differences in the magnitude of the properties predicted by the various functionals, these discrepancies are small compared to the accuracy necessary for most practical applications.« less

Ultra-fast computation of electronic spectra for large systems by tight-binding based simplified Tamm-Dancoff approximation (sTDA-xTB)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grimme, Stefan, E-mail: grimme@thch.uni-bonn.de; Bannwarth, Christoph

2016-08-07

The computational bottleneck of the extremely fast simplified Tamm-Dancoff approximated (sTDA) time-dependent density functional theory procedure [S. Grimme, J. Chem. Phys. 138, 244104 (2013)] for the computation of electronic spectra for large systems is the determination of the ground state Kohn-Sham orbitals and eigenvalues. This limits such treatments to single structures with a few hundred atoms and hence, e.g., sampling along molecular dynamics trajectories for flexible systems or the calculation of chromophore aggregates is often not possible. The aim of this work is to solve this problem by a specifically designed semi-empirical tight binding (TB) procedure similar to the wellmore » established self-consistent-charge density functional TB scheme. The new special purpose method provides orbitals and orbital energies of hybrid density functional character for a subsequent and basically unmodified sTDA procedure. Compared to many previous semi-empirical excited state methods, an advantage of the ansatz is that a general eigenvalue problem in a non-orthogonal, extended atomic orbital basis is solved and therefore correct occupied/virtual orbital energy splittings as well as Rydberg levels are obtained. A key idea for the success of the new model is that the determination of atomic charges (describing an effective electron-electron interaction) and the one-particle spectrum is decoupled and treated by two differently parametrized Hamiltonians/basis sets. The three-diagonalization-step composite procedure can routinely compute broad range electronic spectra (0-8 eV) within minutes of computation time for systems composed of 500-1000 atoms with an accuracy typical of standard time-dependent density functional theory (0.3-0.5 eV average error). An easily extendable parametrization based on coupled-cluster and density functional computed reference data for the elements H–Zn including transition metals is described. The accuracy of the method termed sTDA-xTB is first benchmarked for vertical excitation energies of open- and closed-shell systems in comparison to other semi-empirical methods and applied to exemplary problems in electronic spectroscopy. As side products of the development, a robust and efficient valence electron TB method for the accurate determination of atomic charges as well as a more accurate calculation scheme of dipole rotatory strengths within the Tamm-Dancoff approximation is proposed.« less

Theory of Tunneling Spectroscopy in a Mn12 Single-Electron Transistor by Density-Functional Theory Methods

NASA Astrophysics Data System (ADS)

Michalak, Ł.; Canali, C. M.; Pederson, M. R.; Paulsson, M.; Benza, V. G.

2010-01-01

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.

Theory of tunneling spectroscopy in a Mn12 single-electron transistor by density-functional theory methods.

PubMed

Michalak, Ł; Canali, C M; Pederson, M R; Paulsson, M; Benza, V G

2010-01-08

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.

Electronic transport in organometallic perovskite CH{sub 3}NH{sub 3}PbI{sub 3}: The role of organic cation orientations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berdiyorov, G. R., E-mail: gberdiyorov@qf.org.qa; El-Mellouhi, F.; Madjet, M. E.

Density functional theory in combination with the nonequilibrium Green's function formalism is used to study the electronic transport properties of methylammonium lead-iodide perovskite CH{sub 3}NH{sub 3}PbI{sub 3}. Electronic transport in homogeneous ferroelectric and antiferroelectric phases, both of which do not contain any charged domain walls, is quite similar. The presence of charged domain wall drastically (by about an order of magnitude) enhances the electronic transport in the lateral direction. The increase of the transmission originates from the smaller variation of the electrostatic potential profile along the charged domain walls. This fact may provide a tool for tuning transport properties ofmore » such hybrid materials by manipulating molecular cations having dipole moment.« less

Bands dispersion and charge transfer in β-BeH2

NASA Astrophysics Data System (ADS)

Trivedi, D. K.; Galav, K. L.; Joshi, K. B.

2018-04-01

Predictive capabilities of ab-initio method are utilised to explore bands dispersion and charge transfer in β-BeH2. Investigations are carried out using the linear combination of atomic orbitals method at the level of density functional theory. The crystal structure and related parameters are settled by coupling total energy calculations with the Murnaghan equation of state. Electronic bands dispersion from PBE-GGA is reported. The PBE-GGA, and PBE0 hybrid functional, show that β-BeH2 is a direct gap semiconductor with 1.18 and 2.40 eV band gap. The band gap slowly decreases with pressure and beyond l00 GPa overlap of conduction and valence bands at the r point is observed. Charge transfer is studied by means of Mullikan population analysis.

Emulsifier-free emulsion polymerization produces highly charged, monodisperse particles for near infrared photonic crystals.

PubMed

Reese, Chad E; Asher, Sanford A

2002-04-01

We have developed emulsifier-free, emulsion polymerization recipes for the synthesis of highly charged, monodisperse latex particles of diameters between 500 and 1100 nm. These latexes consist of poly[styrene-(co-2-hydroxyethyl methacrylate)] spherical particles whose surfaces are functionalized with sulfate and carboxylic acid groups. These highly charged, monodisperse particles readily self-assemble into robust, three-dimensionally ordered crystalline colloidal array photonic crystals that Bragg diffract light in the near infrared spectral region. By altering the particle number density, the diffraction wavelength can be tuned from approximately 1000 to approximately 4000 nm.

Orbital-occupancy versus charge ordering and the strength of electron correlations in electron-doped CaMnO3.

PubMed

Luo, Weidong; Franceschetti, Alberto; Varela, Maria; Tao, Jing; Pennycook, Stephen J; Pantelides, Sokrates T

2007-07-20

The structural, electronic, and magnetic properties of mixed-valence compounds are believed to be governed by strong electron correlations. Here we report benchmark density-functional calculations in the spin-polarized generalized-gradient approximation (GGA) for the ground-state properties of doped CaMnO(3). We find excellent agreement with all available data, while inclusion of strong correlations in the GGA+U scheme impairs this agreement. We demonstrate that formal oxidation states reflect only orbital occupancies, not charge transfer, and resolve outstanding controversies about charge ordering.

Orbital-Occupancy versus Charge Ordering and the Strength of Electron Correlations in Electron-Doped CaMnO3

NASA Astrophysics Data System (ADS)

Luo, Weidong; Franceschetti, Alberto; Varela, Maria; Tao, Jing; Pennycook, Stephen J.; Pantelides, Sokrates T.

2007-07-01

The structural, electronic, and magnetic properties of mixed-valence compounds are believed to be governed by strong electron correlations. Here we report benchmark density-functional calculations in the spin-polarized generalized-gradient approximation (GGA) for the ground-state properties of doped CaMnO3. We find excellent agreement with all available data, while inclusion of strong correlations in the GGA+U scheme impairs this agreement. We demonstrate that formal oxidation states reflect only orbital occupancies, not charge transfer, and resolve outstanding controversies about charge ordering.

Wigner functions for fermions in strong magnetic fields

NASA Astrophysics Data System (ADS)

Sheng, Xin-li; Rischke, Dirk H.; Vasak, David; Wang, Qun

2018-02-01

We compute the covariant Wigner function for spin-(1/2) fermions in an arbitrarily strong magnetic field by exactly solving the Dirac equation at non-zero fermion-number and chiral-charge densities. The Landau energy levels as well as a set of orthonormal eigenfunctions are found as solutions of the Dirac equation. With these orthonormal eigenfunctions we construct the fermion field operators and the corresponding Wigner-function operator. The Wigner function is obtained by taking the ensemble average of the Wigner-function operator in global thermodynamical equilibrium, i.e., at constant temperature T and non-zero fermion-number and chiral-charge chemical potentials μ and μ_5, respectively. Extracting the vector and axial-vector components of the Wigner function, we reproduce the currents of the chiral magnetic and separation effect in an arbitrarily strong magnetic field.

Quantification of surface charge density and its effect on boundary slip.

PubMed

Jing, Dalei; Bhushan, Bharat

2013-06-11

Reduction of fluid drag is important in the micro-/nanofluidic systems. Surface charge and boundary slip can affect the fluid drag, and surface charge is also believed to affect boundary slip. The quantification of surface charge and boundary slip at a solid-liquid interface has been widely studied, but there is a lack of understanding of the effect of surface charge on boundary slip. In this paper, the surface charge density of borosilicate glass and octadecyltrichlorosilane (OTS) surfaces immersed in saline solutions with two ionic concentrations and deionized (DI) water with different pH values and electric field values is quantified by fitting experimental atomic force microscopy (AFM) electrostatic force data using a theoretical model relating the surface charge density and electrostatic force. Results show that pH and electric field can affect the surface charge density of glass and OTS surfaces immersed in saline solutions and DI water. The mechanisms of the effect of pH and electric field on the surface charge density are discussed. The slip length of the OTS surface immersed in saline solutions with two ionic concentrations and DI water with different pH values and electric field values is measured, and their effects on the slip length are analyzed from the point of surface charge. Results show that a larger absolute value of surface charge density leads to a smaller slip length for the OTS surface.

Computational studies of molecular charge transfer complexes of heterocyclic 4-methylepyridine-2-azomethine-p-benzene derivatives with picric acid and m-dinitrobenzene.

PubMed

Al-Harbi, L M; El-Mossalamy, E H; Obaid, A Y; Al-Jedaani, A H

2014-01-01

Charge transfer complexes of substituted aryl Schiff bases as donors with picric acid and m-dinitrobenzene as acceptors were investigated by using computational analysis calculated by Configuration Interaction Singles Hartree-Fock (CIS-HF) at standard 6-31G∗ basis set and Time-Dependent Density-Functional Theory (TD-DFT) levels of theory at standard 6-31G∗∗ basis set, infrared spectra, visible and nuclear magnetic resonance spectra are investigated. The optimized geometries and vibrational frequencies were evaluated. The energy and oscillator strength were calculated by Configuration Interaction Singles Hartree-Fock method (CIS-HF) and the Time-Dependent Density-Functional Theory (TD-DFT) results. Electronic properties, such as HOMO and LUMO energies and band gaps of CTCs set, were studied by the Time-Dependent density functional theory with Becke-Lee-Young-Parr (B3LYP) composite exchange correlation functional and by Configuration Interaction Singles Hartree-Fock method (CIS-HF). The ionization potential Ip and electron affinity EA were calculated by PM3, HF and DFT methods. The columbic force was calculated theoretically by using (CIS-HF and TD-DFT) methods. This study confirms that the theoretical calculation of vibrational frequencies for (aryl Schiff bases--(m-dinitrobenzene and picric acid)) complexes are quite useful for the vibrational assignment and for predicting new vibrational frequencies. Copyright © 2013 Elsevier B.V. All rights reserved.

Reliability of gamma-irradiated n-channel ZnO thin-film transistors: electronic and interface properties

NASA Astrophysics Data System (ADS)

Lee, Kin Kiong; Wang, Danna; Shinobu, Onoda; Ohshima, Takeshi

2018-04-01

Radiation-induced charge trapping and interface traps in n-channel ZnO thin film transistors are characterised as a function of total dose and irradiation bias following exposure to gamma-rays. Devices were irradiated up to ∼60 kGy(SiO?) and the electrical characteristic exhibits two distinct regimes. In the first regime, up to a total dose of 40 kGy(SiO?), the threshold voltage increases positively. However, in the second regime with irradiation greater than 40 kGy(SiO?), the threshold voltage moves in the opposite direction. This reversal of threshold voltage is attributed to the influence of the radiation-induced interface and oxide- charge, in which both have opposite polarity, on the electrical performance of the transistors. In the first regime, the generation of the oxide- charge is initially greater than the density of interface traps and caused a positive shift. In the second regime, when the total doses were greater than 40 kGy(SiO?), the radiation-induced interface traps are greater than the density of oxide- charge and caused the threshold voltage to switch direction. Further, the generated interface traps contributed to the degradation of the effective channel mobility, whereas the density of traps at the grain-boundaries did not increase significantly upon irradiation. Isothermal annealing of the devices at 363 K results in a reduction in the trap density and an improvement of the effective channel mobility to ∼90% of its pre-irradiation value.

Tuning the photoluminescence of graphene quantum dots through the charge transfer effect of functional groups.

PubMed

Jin, Sung Hwan; Kim, Da Hye; Jun, Gwang Hoon; Hong, Soon Hyung; Jeon, Seokwoo

2013-02-26

The band gap properties of graphene quantum dots (GQDs) arise from quantum confinement effects and differ from those in semimetallic graphene sheets. Tailoring the size of the band gap and understanding the band gap tuning mechanism are essential for the applications of GQDs in opto-electronics. In this study, we observe that the photoluminescence (PL) of the GQDs shifts due to charge transfers between functional groups and GQDs. GQDs that are functionalized with amine groups and are 1-3 layers thick and less than 5 nm in diameter were successfully fabricated using a two-step cutting process from graphene oxides (GOs). The functionalized GQDs exhibit a redshift of PL emission (ca. 30 nm) compared to the unfunctionalized GQDs. Furthermore, the PL emissions of the GQDs and the amine-functionalized GQDs were also shifted by changes in the pH due to the protonation or deprotonation of the functional groups. The PL shifts resulted from charge transfers between the functional groups and GQDs, which can tune the band gap of the GQDs. Calculations from density functional theory (DFT) are in good agreement with our proposed mechanism for band gap tuning in the GQDs through the use of functionalization.

An ab-initio investigation on SrLa intermetallic compound

NASA Astrophysics Data System (ADS)

Kumar, S. Ramesh; Jaiganesh, G.; Jayalakshmi, V.

2018-05-01

The electronic, elastic and thermodynamic property of CsCl-type SrLa are investigated through density functional theory. The energy-volume relation for this compound has been obtained. The band structure, density of states and charge density in (110) plane are also examined. The elastic constants (C11, C12 and C44) of SrLa is computed, then, using these elastic constants, the bulk moduli, shear moduli, Young's moduli and Poisson's ratio are also derived. The calculated results showed that CsCl-type SrLa is ductile at ambient conditions. The thermodynamic quantities such as free energy, entropy and heat capacity as a function of temperature are estimated and the results obtained are discussed.

Recombination dynamics in In{sub x}Ga{sub 1−x}N quantum wells—Contribution of excited subband recombination to carrier leakage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulz, T.; Markurt, T.; Albrecht, M.

2014-11-03

The recombination dynamics of In{sub x}Ga{sub 1−x}N single quantum wells are investigated. By comparing the photoluminescence (PL) decay spectra with simulated emission spectra obtained by a Schrödinger-Poisson approach, we give evidence that recombination from higher subbands contributes the emission of the quantum well at high excitation densities. This recombination path appears as a shoulder on the high energy side of the spectrum at high charge carrier densities and exhibits decay in the range of ps. Due to the lower confinement of the excited subband states, a distinct proportion of the probability density function lies outside the quantum well, thus contributingmore » to charge carrier loss. By estimating the current density in our time resolved PL experiments, we show that the onset of this loss mechanism occurs in the droop relevant regime above 20 A/cm{sup 2}.« less

Two symmetric n-type interfaces SrTiO{sub 3}/LaAlO{sub 3} in perovskite: Electronic properties from density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reshak, A. H., E-mail: maalidph@yahoo.co.uk, E-mail: mabujafar@najah.edu; Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis; Abu-Jafar, M. S., E-mail: maalidph@yahoo.co.uk, E-mail: mabujafar@najah.edu

2016-06-28

The first principles study of the (001) two symmetric n-type interfaces between two insulating perovskites, the nonpolar SrTiO{sub 3} (STO), and the polar LaAlO{sub 3} (LAO) was performed. We have analyzed the formation of metallic interface states between the STO and LAO heterointerfaces by using the all-electron full-potential linearized augmented plane-wave approach based on the density functional theory, within the local density approximation, the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA), and the Engel-Vosko GGA (EVGGA) formalism. It has been found that some bands cross the Fermi energy level (E{sub F}), forming a metallic nature of two symmetric n-type 6.5STO/1.5LAO interfaces withmore » density of states at E{sub F}, N(E{sub F}) of about 3.56 (state/eV/unit cell), and bare electronic specific heat coefficient (γ) of about 0.62 mJ/(mol cell K{sup 2}). The electronic band stature and the partial density of states in the vicinity of E{sub F} are mainly originated from Ti1,2,3,4-3dxy orbitals. These bands are responsible for the metallic behavior and the forming of the Fermi surface of the two symmetric n-type 6.5STO/1.5LAO interfaces. To obtain a clear map of the valence band electronic charge density distribution of the two symmetric n-type 6.5STO/1.5LAO interfaces, we have investigated the bond's nature and the interactions between the atoms. It reveals that the charge is attracted towards O atoms as it is clear that the O atoms are surrounded by uniform blue spheres which indicate the maximum charge accumulation.« less

Quantum dynamics of charge state in silicon field evaporation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silaeva, Elena P.; Uchida, Kazuki; Watanabe, Kazuyuki, E-mail: kazuyuki@rs.kagu.tus.ac.jp

2016-08-15

The charge state of an ion field-evaporating from a silicon-atom cluster is analyzed using time-dependent density functional theory coupled to molecular dynamics. The final charge state of the ion is shown to increase gradually with increasing external electrostatic field in agreement with the average charge state of silicon ions detected experimentally. When field evaporation is triggered by laser-induced electronic excitations the charge state also increases with increasing intensity of the laser pulse. At the evaporation threshold, the charge state of the evaporating ion does not depend on the electrostatic field due to the strong contribution of laser excitations to themore » ionization process both at low and high laser energies. A neutral silicon atom escaping the cluster due to its high initial kinetic energy is shown to be eventually ionized by external electrostatic field.« less

Interactions between cells and ionized dendritic biomaterials: Flow cytometry and fluorescence spectroscopic studies

NASA Astrophysics Data System (ADS)

Kannan, R. M.; Kolhe, Parag; Khandare, Jayant; Kannan, Sujatha; Lieh-Lai, Mary

2004-03-01

Dendrimers and hyperbranched polymers are a new class of macromolecules characterized by large density of "tunable" peripheral functional groups. Therefore dendrimers can serve as a model macromolecular system to study the influence of molecular geometry and charge density on transport across biological barriers, especially cellular interfaces. The effect of size, end-functionality, surface charge (pH), and the nature of the cell surface are expected to play an important role in transport, and are investigated using flow cytometry, fluorescene microscopy and UV/Vis spectroscopy. Our results suggest that at physiological pH, cationic polyamidoamine (PAMAM) dendrimers can enter the A549 cancer lung epithelial cells within 5 minutes, perhaps due to the favorable interaction between anionic surface receptors of cells and cationic PAMAM dendrimer, through adsorptive endocytosis. On the other hand, hyperbranched polyol, which is a neutral polymer at physiological pH, enters cells at a much slower rate. The entry of hyperbranched polyol may be because of fluid-phase pinocytosis. Our results also indicate that the dendritic polymers enter the cell surface much more rapidly than linear polymers, and some small drugs, suggesting that the high density of functional groups plays a key role in the interaction with the cell surface, and the subsequent transport inside.

Adenine-functionalized Spongy Graphene for Green and High-Performance Supercapacitors

PubMed Central

El-Gendy, Dalia M.; Ghany, Nabil A. Abdel; El Sherbini, E. E. Foad; Allam, Nageh K.

2017-01-01

A simple method is demonstrated to prepare spongy adenine-functionalized graphene (SFG) as interconnected, porous 3-dimensional (3D) network crinkly sheets. Such 3D network structure provides better contact at the electrode/electrolyte interface and facilitates the charge transfer kinetics. The fabricated SFG was characterized by X-ray diffraction (XRD), FTIR, scanning electron microscopy (FESEM), Raman spectroscopy, thermogravimetric analysis (TGA), UV−vis absorption spectroscopy, and transmission electron microscopy (TEM). The synthesized materials have been evaluated as supercapacitor materials in 0.5 M H2SO4 using cyclic voltammetry (CV) at different potential scan rates, and galvanostatic charge/discharge tests at different current densities. The SFG electrodes showed a maximum specific capacitance of 333 F/g at scan rate of 1 mV/s and exhibited excellent cycling retention of 102% after 1000 cycles at 200 mV/s. The energy density was 64.42 Wh/kg with a power density of 599.8 W/kg at 1.0 A/g. Those figures of merit are much higher than those reported for graphene-based materials tested under similar conditions. The observed high performance can be related to the synergistic effects of the spongy structure and the adenine functionalization. PMID:28216668

On contribution of known atomic partial charges of protein backbone in electrostatic potential density maps.

PubMed

Wang, Jimin

2017-06-01

Partial charges of atoms in a molecule and electrostatic potential (ESP) density for that molecule are known to bear a strong correlation. In order to generate a set of point-field force field parameters for molecular dynamics, Kollman and coworkers have extracted atomic partial charges for each of all 20 amino acids using restrained partial charge-fitting procedures from theoretical ESP density obtained from condensed-state quantum mechanics. The magnitude of atomic partial charges for neutral peptide backbone they have obtained is similar to that of partial atomic charges for ionized carboxylate side chain atoms. In this study, the effect of these known atomic partial charges on ESP is examined using computer simulations and compared with the experimental ESP density recently obtained for proteins using electron microscopy. It is found that the observed ESP density maps are most consistent with the simulations that include atomic partial charges of protein backbone. Therefore, atomic partial charges are integral part of atomic properties in protein molecules and should be included in model refinement. © 2017 The Protein Society.

Effect of 30 MeV Li3+ ion and 8 MeV electron irradiation on N-channel MOSFETs

NASA Astrophysics Data System (ADS)

Prakash, A. P. G.; Ganesh, K. C. P.; Nagesha, Y. N.; Umakanth, D.; Arora, S. K.; Siddappa, K.

The effect of 30 MeV Li3+ ion and 8 MeV electron irradiation on the threshold voltage (V-TH), the voltage shift due to interface trapped charge (DeltaV(Nit)), the voltage shift due to oxide trapped charge (DeltaV(Not)), the density of interface trapped charge (DeltaN(it)), the density of oxide trapped charge (DeltaN(ot) ) and the drain saturation current (I-D Sat) were studied as a function of fluence. Considerable increase in DeltaN(it) and DeltaN(ot) , and decrease in V-TH and I-D Sat were observed in both types of irradiation. The observed difference in the properties of Li3+ ion and electron irradiated MOSFETs are interpreted on the basis of energy loss process associated with the type of radiation. The study showed that the 30 MeV Li3+ ion irradiation produce more damage when compared to the 8 MeV electron irradiation because of the higher electronic energy loss value. High temperature annealing studies showed that trapped charge generated during ion and electron irradiation was annealed out at 500 degreesC.

Atomic and electronic structure of trilayer graphene/SiC(0001): Evidence of Strong Dependence on Stacking Sequence and charge transfer.

PubMed

Pierucci, Debora; Brumme, Thomas; Girard, Jean-Christophe; Calandra, Matteo; Silly, Mathieu G; Sirotti, Fausto; Barbier, Antoine; Mauri, Francesco; Ouerghi, Abdelkarim

2016-09-15

The transport properties of few-layer graphene are the directly result of a peculiar band structure near the Dirac point. Here, for epitaxial graphene grown on SiC, we determine the effect of charge transfer from the SiC substrate on the local density of states (LDOS) of trilayer graphene using scaning tunneling microscopy/spectroscopy and angle resolved photoemission spectroscopy (ARPES). Different spectra are observed and are attributed to the existence of two stable polytypes of trilayer: Bernal (ABA) and rhomboedreal (ABC) staking. Their electronic properties strongly depend on the charge transfer from the substrate. We show that the LDOS of ABC stacking shows an additional peak located above the Dirac point in comparison with the LDOS of ABA stacking. The observed LDOS features, reflecting the underlying symmetry of the two polytypes, were reproduced by explicit calculations within density functional theory (DFT) including the charge transfer from the substrate. These findings demonstrate the pronounced effect of stacking order and charge transfer on the electronic structure of trilayer or few layer graphene. Our approach represents a significant step toward understand the electronic properties of graphene layer under electrical field.

Molecularly Engineered Azobenzene Derivatives for High Energy Density Solid-State Solar Thermal Fuels.

PubMed

Cho, Eugene N; Zhitomirsky, David; Han, Grace G D; Liu, Yun; Grossman, Jeffrey C

2017-03-15

Solar thermal fuels (STFs) harvest and store solar energy in a closed cycle system through conformational change of molecules and can release the energy in the form of heat on demand. With the aim of developing tunable and optimized STFs for solid-state applications, we designed three azobenzene derivatives functionalized with bulky aromatic groups (phenyl, biphenyl, and tert-butyl phenyl groups). In contrast to pristine azobenzene, which crystallizes and makes nonuniform films, the bulky azobenzene derivatives formed uniform amorphous films that can be charged and discharged with light and heat for many cycles. Thermal stability of the films, a critical metric for thermally triggerable STFs, was greatly increased by the bulky functionalization (up to 180 °C), and we were able to achieve record high energy density of 135 J/g for solid-state STFs, over a 30% improvement compared to previous solid-state reports. Furthermore, the chargeability in the solid state was improved, up to 80% charged from 40% charged in previous solid-state reports. Our results point toward molecular engineering as an effective method to increase energy storage in STFs, improve chargeability, and improve the thermal stability of the thin film.

Combined ab initio and density functional study on polaron to bipolaron transitions in oligophenyls and oligothiophenes

NASA Astrophysics Data System (ADS)

Irle, Stephan; Lischka, Hans

1997-08-01

Ab initio self-consistent-field (SCF), two-configuration SCF (TCSCF), and density functional theory (DFT) calculations on the charge-transfer complexes of doubly Li/Cl-doped oligothiophenes and oligo(p-phenyls) and on respective charged systems without counterions have been carried out in order to study polaron to bipolaron transitions. Oligomer chains up to octamers and the ring structures cyclo-dodecathiophene and cyclo-dodeca(p-phenyl) have been investigated. Special attention is paid to the open-shell biradical character of two isolated polaronic defects. It is found that the TCSCF and the spin-unrestricted DFT methods can be successfully applied. A bipolaron structure is obtained when the doping atoms are located on neighboring rings and when there is one undoped ring separating the two doped ones. If there are two or more undoped rings in between a two-polaron configuration (biradical) is found. The bipolaron system is calculated to be more stable than the two-polaron case when counterions are taken into account. The stabilities are reversed if the bare, doubly-charged systems are considered. A theoretical estimate for the barrier height of the polaron to bipolaron transition is given using model reaction coordinates.

Vibration responses of h-BN sheet to charge doping and external strain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Wei; Yang, Yu; Zheng, Fawei

2013-12-07

Based on density functional theory and density functional perturbation theory calculations, we systematically investigate the vibration responses of h-BN sheet to charge doping and external strains. It is found that under hole doping, the phonon frequencies of the ZO and TO branches at different wave vector q shift linearly with different slopes. Under electron doping, although the phonon frequencies shift irregularly, the shifting values are different at different phonon wave vectors. Interestingly, we find that external strain can restrain the irregular vibration responses of h-BN sheet to electron doping. The critical factor is revealed to be the relative position ofmore » the nearly free electron and boron p{sub z} states of h-BN sheet. Under external strains, the vibration responses of h-BN sheet are also found to be highly dependent on the phonon branches. Different vibration modes at different q points are revealed to be responsible for the vibration responses of h-BN sheet to charge doping and external strain. Our results point out a new way to detect the doping or strain status of h-BN sheet by measuring the vibration frequencies at different wave vector.« less

UV-Vis spectroscopy and density functional study of solvent effect on the charge transfer band of the n → σ* complexes of 2-Methylpyridine and 2-Chloropyridine with molecular iodine

NASA Astrophysics Data System (ADS)

Gogoi, Pallavi; Mohan, Uttam; Borpuzari, Manash Protim; Boruah, Abhijit; Baruah, Surjya Kumar

2017-03-01

UV-Vis spectroscopy has established that Pyridine substitutes form n→σ* charge transfer (CT) complexes with molecular Iodine. This study is a combined approach of purely experimental UV-Vis spectroscopy, Multiple linear regression theory and Computational chemistry to analyze the effect of solvent upon the charge transfer band of 2-Methylpyridine-I2 and 2-Chloropyridine-I2 complexes. Regression analysis verifies the dependence of the CT band upon different solvent parameters. Dielectric constant and refractive index are considered among the bulk solvent parameters and Hansen, Kamlet and Catalan parameters are taken into consideration at the molecular level. Density Functional Theory results explain well the blue shift of the CT bands in polar medium as an outcome of stronger donor acceptor interaction. A logarithmic relation between the bond length of the bridging atoms of the donor and the acceptor with the dielectric constant of the medium is established. Tauc plot and TDDFT study indicates a non-vertical electronic transition in the complexes. Buckingham and Lippert Mataga equations are applied to check the Polarizability effect on the CT band.

Density functional theory of electron transfer beyond the Born-Oppenheimer approximation: Case study of LiF

NASA Astrophysics Data System (ADS)

Li, Chen; Requist, Ryan; Gross, E. K. U.

2018-02-01

We perform model calculations for a stretched LiF molecule, demonstrating that nonadiabatic charge transfer effects can be accurately and seamlessly described within a density functional framework. In alkali halides like LiF, there is an abrupt change in the ground state electronic distribution due to an electron transfer at a critical bond length R = Rc, where an avoided crossing of the lowest adiabatic potential energy surfaces calls the validity of the Born-Oppenheimer approximation into doubt. Modeling the R-dependent electronic structure of LiF within a two-site Hubbard model, we find that nonadiabatic electron-nuclear coupling produces a sizable elongation of the critical Rc by 0.5 bohr. This effect is very accurately captured by a simple and rigorously derived correction, with an M-1 prefactor, to the exchange-correlation potential in density functional theory, M = reduced nuclear mass. Since this nonadiabatic term depends on gradients of the nuclear wave function and conditional electronic density, ∇Rχ(R) and ∇Rn(r, R), it couples the Kohn-Sham equations at neighboring R points. Motivated by an observed localization of nonadiabatic effects in nuclear configuration space, we propose a local conditional density approximation—an approximation that reduces the search for nonadiabatic density functionals to the search for a single function y(n).

Quasiparticle and hybrid density functional methods in defect studies: An application to the nitrogen vacancy in GaN

NASA Astrophysics Data System (ADS)

Lewis, D. K.; Matsubara, M.; Bellotti, E.; Sharifzadeh, S.

2017-12-01

Defects in semiconductors can play a vital role in the performance of electronic devices, with native defects often dominating the electronic properties of the semiconductor. Understanding the relationship between structural defects and electronic function will be central to the design of new high-performance materials. In particular, it is necessary to quantitatively understand the energy and lifetime of electronic states associated with the defect. Here, we apply first-principles density functional theory (DFT) and many-body perturbation theory within the GW approximation to understand the nature and energy of the defect states associated with a charged nitrogen vacancy on the electronic properties of gallium nitride (GaN), as a model of a well-studied and important wide gap semiconductor grown with defects. We systematically investigate the sources of error associated with the GW approximation and the role of the underlying atomic structure on the predicted defect state energies. Additionally, analysis of the computed electronic density of states (DOS) reveals that there is one occupied defect state 0.2 eV below the valence band maximum and three unoccupied defect states at energy of 0.2-0.4 eV above the conduction band minimum, suggesting that this defect in the +1 charge state will not behave as a carrier trap. Furthermore, we compare the character and energy of the defect state obtained from GW and DFT using the HSE approximate density functional and find excellent agreement. This systematic study provides a more complete understanding of how to obtain quantitative defect energy states in bulk semiconductors.

Crystal-field splittings in rare-earth-based hard magnets: An ab initio approach

NASA Astrophysics Data System (ADS)

Delange, Pascal; Biermann, Silke; Miyake, Takashi; Pourovskii, Leonid

2017-10-01

We apply the first-principles density functional theory + dynamical mean-field theory framework to evaluate the crystal-field splitting on rare-earth sites in hard magnetic intermetallics. An atomic (Hubbard-I) approximation is employed for local correlations on the rare-earth 4 f shell and self-consistency in the charge density is implemented. We reduce the density functional theory self-interaction contribution to the crystal-field splitting by properly averaging the 4 f charge density before recalculating the one-electron Kohn-Sham potential. Our approach is shown to reproduce the experimental crystal-field splitting in the prototypical rare-earth hard magnet SmCo5. Applying it to R Fe12 and R Fe12X hard magnets (R =Nd , Sm and X =N , Li), we obtain in particular a large positive value of the crystal-field parameter A20〈r2〉 in NdFe12N resulting in a strong out-of-plane anisotropy observed experimentally. The sign of A20〈r2〉 is predicted to be reversed by substituting N with Li, leading to a strong out-of-plane anisotropy in SmFe12Li . We discuss the origin of this strong impact of N and Li interstitials on the crystal-field splitting on rare-earth sites.

Competition of density waves and quantum multicritical behavior in Dirac materials from functional renormalization

NASA Astrophysics Data System (ADS)

Classen, Laura; Herbut, Igor F.; Janssen, Lukas; Scherer, Michael M.

2016-03-01

We study the competition of spin- and charge-density waves and their quantum multicritical behavior for the semimetal-insulator transitions of low-dimensional Dirac fermions. Employing the effective Gross-Neveu-Yukawa theory with two order parameters as a model for graphene and a growing number of other two-dimensional Dirac materials allows us to describe the physics near the multicritical point at which the semimetallic and the spin- and charge-density-wave phases meet. With the help of a functional renormalization group approach, we are able to reveal a complex structure of fixed points, the stability properties of which decisively depend on the number of Dirac fermions Nf. We give estimates for the critical exponents and observe crucial quantitative corrections as compared to the previous first-order ɛ expansion. For small Nf, the universal behavior near the multicritical point is determined by the chiral Heisenberg universality class supplemented by a decoupled, purely bosonic, Ising sector. At large Nf, a novel fixed point with nontrivial couplings between all sectors becomes stable. At intermediate Nf, including the graphene case (Nf=2 ), no stable and physically admissible fixed point exists. Graphene's phase diagram in the vicinity of the intersection between the semimetal, antiferromagnetic, and staggered density phases should consequently be governed by a triple point exhibiting first-order transitions.

Charge density on thin straight wire, revisited

NASA Astrophysics Data System (ADS)

Jackson, J. D.

2000-09-01

The question of the equilibrium linear charge density on a charged straight conducting "wire" of finite length as its cross-sectional dimension becomes vanishingly small relative to the length is revisited in our didactic presentation. We first consider the wire as the limit of a prolate spheroidal conductor with semi-minor axis a and semi-major axis c when a/c<<1. We then treat an azimuthally symmetric straight conductor of length 2c and variable radius r(z) whose scale is defined by a parameter a. A procedure is developed to find the linear charge density λ(z) as an expansion in powers of 1/Λ, where Λ≡ln(4c2/a2), beginning with a uniform line charge density λ0. We show, for this rather general wire, that in the limit Λ>>1 the linear charge density becomes essentially uniform, but that the tiny nonuniformity (of order 1/Λ) is sufficient to produce a tangential electric field (of order Λ0) that cancels the zeroth-order field that naively seems to belie equilibrium. We specialize to a right circular cylinder and obtain the linear charge density explicitly, correct to order 1/Λ2 inclusive, and also the capacitance of a long isolated charged cylinder, a result anticipated in the published literature 37 years ago. The results for the cylinder are compared with published numerical computations. The second-order correction to the charge density is calculated numerically for a sampling of other shapes to show that the details of the distribution for finite 1/Λ vary with the shape, even though density becomes constant in the limit Λ→∞. We give a second method of finding the charge distribution on the cylinder, one that approximates the charge density by a finite polynomial in z2 and requires the solution of a coupled set of linear algebraic equations. Perhaps the most striking general observation is that the approach to uniformity as a/c→0 is extremely slow.

Reactivity of etoricoxib based on computational study of molecular orbitals, molecular electrostatic potential surface and Mulliken charge analysis

NASA Astrophysics Data System (ADS)

Sachdeva, Ritika; Soni, Abhinav; Singh, V. P.; Saini, G. S. S.

2018-05-01

Etoricoxib is one of the selective cyclooxygenase inhibitor drug which plays a significant role in the pharmacological management of arthritis and pain. The theoretical investigation of its reactivity is done using Density Functional Theory calculations. Molecular Electrostatic Potential Surface of etoricoxib and its Mulliken atomic charge distribution are used for the prediction of its electrophilic and nucleophilic sites. The detailed analysis of its frontier molecular orbitals is also done.

Convergence of Ground and Excited State Properties of Divacancy Defects in 4H-SiC with Computational Cell Size

DTIC Science & Technology

2018-03-01

computational parameters needs to be established. We used density functional theory to compute defect formation energies of the neutral and charged hh... energies for the 3A to 3E transition (absorption, zero phonon lines, and emission), which is essential for optical initialization and read-out. We...PBE, defect formation energy , charge transition levels, absorption, zero phonon lines, emission 16. SECURITY CLASSIFICATION OF: 17. LIMITATION

Valence and charge-transfer optical properties for some SinCm (m, n ≤ 12) clusters: Comparing TD-DFT, complete-basis-limit EOMCC, and benchmarks from spectroscopy.

PubMed

Lutz, Jesse J; Duan, Xiaofeng F; Ranasinghe, Duminda S; Jin, Yifan; Margraf, Johannes T; Perera, Ajith; Burggraf, Larry W; Bartlett, Rodney J

2018-05-07

Accurate optical characterization of the closo-Si 12 C 12 molecule is important to guide experimental efforts toward the synthesis of nano-wires, cyclic nano-arrays, and related array structures, which are anticipated to be robust and efficient exciton materials for opto-electronic devices. Working toward calibrated methods for the description of closo-Si 12 C 12 oligomers, various electronic structure approaches are evaluated for their ability to reproduce measured optical transitions of the SiC 2 , Si 2 C n (n = 1-3), and Si 3 C n (n = 1, 2) clusters reported earlier by Steglich and Maier [Astrophys. J. 801, 119 (2015)]. Complete-basis-limit equation-of-motion coupled-cluster (EOMCC) results are presented and a comparison is made between perturbative and renormalized non-iterative triples corrections. The effect of adding a renormalized correction for quadruples is also tested. Benchmark test sets derived from both measurement and high-level EOMCC calculations are then used to evaluate the performance of a variety of density functionals within the time-dependent density functional theory (TD-DFT) framework. The best-performing functionals are subsequently applied to predict valence TD-DFT excitation energies for the lowest-energy isomers of Si n C and Si n-1 C 7-n (n = 4-6). TD-DFT approaches are then applied to the Si n C n (n = 4-12) clusters and unique spectroscopic signatures of closo-Si 12 C 12 are discussed. Finally, various long-range corrected density functionals, including those from the CAM-QTP family, are applied to a charge-transfer excitation in a cyclic (Si 4 C 4 ) 4 oligomer. Approaches for gauging the extent of charge-transfer character are also tested and EOMCC results are used to benchmark functionals and make recommendations.

Emission current from a single micropoint of explosive emission cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ping; Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024; Sun, Jun

Explosive emission cathodes (EECs) are widely used due to their large current. There has been much research on the explosive electron emission mechanism demonstrating that a current density of 10{sup 8}–10{sup 9 }A/cm{sup 2} is necessary for a micropoint to explode in several nanoseconds and the micropoint size is in micron-scale according to the observation of the cathode surface. This paper, however, makes an effort to research the current density and the micropoint size in another way which considers the space charge screening effect. Our model demonstrates that the relativistic effect is insignificant for the micropoint emission due to the smallmore » size of the micropoint and uncovers that the micron-scale size is an intrinsic demand for the micropoint to reach a space charge limited current density of 10{sup 8}–10{sup 9 }A/cm{sup 2}. Meanwhile, our analysis shows that as the voltage increases, the micropoint emission will turn from a field limited state to a space charge limited state, which makes the steady-state micropoint current density independent of the cathode work function and much less dependent on the electric field and the field enhancement factor than that predicted by the Fowler-Nordheim formula.« less

The experimental charge-density approach in the evaluation of intermolecular interactions. Application of a new module of the XD programming package to several solids including a pentapeptide.

PubMed

Abramov, Y A; Volkov, A; Wu, G; Coppens, P

2000-11-01

A new module interfaced to the XD programming package has been used in the evaluation of intermolecular interactions and lattice energies of the crystals of p-nitroaniline, L-asparagine monohydrate and the pentapeptide Boc-Gln-D-Iva-Hyp-Ala-Phol (Boc = butoxycarbonyl, Iva = isovaline = ethylalanine, Phol = phenylalaninol). The electrostatic interactions are evaluated with the atom-centered distributed multipoles from KRMM (kappa'-restricted multipole model) refinements, using the Buckingham expression for non-overlapping charge densities. Results for p-nitroaniline are compared with Hartree-Fock (HF), density functional (DFT) and Moller-Plesset (MP2) supermolecular calculations and with HF and DFT periodic calculations. The HF and DFT methods fail to predict the stability of the p-nitroaniline crystal but the results of the experimental charge-density approach (ECDA) are in good agreement with both MP2 interaction energies and the experimental lattice energy. ECDA results for L-asparagine monohydrate compare well with those from DFT supermolecular and periodic HF calculations. The disorder of the terminal group in the pentapeptide, which persists at the experimental temperature of 20 K, corresponds to an energy difference of only 0.35 kJ mol(-1), which is too small to be reproduced with current methods.

Edge effects in vertically-oriented graphene based electric double-layer capacitors

NASA Astrophysics Data System (ADS)

Yang, Huachao; Yang, Jinyuan; Bo, Zheng; Zhang, Shuo; Yan, Jianhua; Cen, Kefa

2016-08-01

Vertically-oriented graphenes (VGs) have been demonstrated as a promising active material for electric double-layer capacitors (EDLCs), partially due to their edge-enriched structure. In this work, the 'edge effects', i.e., edges as the promoters of high capacitance, in VG based EDLCs are investigated with experimental research and numerical simulations. VGs with diverse heights (i.e., edge-to-basal ratios) and edge densities are prepared with varying the plasma-enabled growth time and employing different plasma sources. Electrochemical measurements show that the edges play a predominant role on the charge storage behavior of VGs. A simulation is further conducted to unveil the roles of the edges on the separation and adsorption of ions within VG channels. The initial charge distribution of a VG plane is obtained with density functional theory (DFT) calculations, which is subsequently applied to a molecular dynamics (MD) simulation system to gain the insights into the microscope EDLC structures. Compared with the basal planes, the edges present higher initial charge density (by 4.2 times), higher ion packing density (by 2.6 times), closer ion packing location (by 0.8 Å), and larger ion separation degree (by 14%). The as-obtained findings will be instructive in designing the morphology and structure of VGs for enhanced capacitive performances.

A nonadditive methanol force field: Bulk liquid and liquid-vapor interfacial properties via molecular dynamics simulations using a fluctuating charge model

NASA Astrophysics Data System (ADS)

Patel, Sandeep; Brooks, Charles L.

2005-01-01

We study the bulk and interfacial properties of methanol via molecular dynamics simulations using a CHARMM (Chemistry at HARvard Molecular Mechanics) fluctuating charge force field. We discuss the parametrization of the electrostatic model as part of the ongoing CHARMM development for polarizable protein force fields. The bulk liquid properties are in agreement with available experimental data and competitive with existing fixed-charge and polarizable force fields. The liquid density and vaporization enthalpy are determined to be 0.809 g/cm3 and 8.9 kcal/mol compared to the experimental values of 0.787 g/cm3 and 8.94 kcal/mol, respectively. The liquid structure as indicated by radial distribution functions is in keeping with the most recent neutron diffraction results; the force field shows a slightly more ordered liquid, necessarily arising from the enhanced condensed phase electrostatics (as evidenced by an induced liquid phase dipole moment of 0.7 D), although the average coordination with two neighboring molecules is consistent with the experimental diffraction study as well as with recent density functional molecular dynamics calculations. The predicted surface tension of 19.66±1.03 dyn/cm is slightly lower than the experimental value of 22.6 dyn/cm, but still competitive with classical force fields. The interface demonstrates the preferential molecular orientation of molecules as observed via nonlinear optical spectroscopic methods. Finally, via canonical molecular dynamics simulations, we assess the model's ability to reproduce the vapor-liquid equilibrium from 298 to 423 K, the simulation data then used to obtain estimates of the model's critical temperature and density. The model predicts a critical temperature of 470.1 K and critical density of 0.312 g/cm3 compared to the experimental values of 512.65 K and 0.279 g/cm3, respectively. The model underestimates the critical temperature by 8% and overestimates the critical density by 10%, and in this sense is roughly equivalent to the underlying fixed-charge CHARMM22 force field.

Determination of the surface charge density and temperature dependence of purple membrane by electric force microscopy.

PubMed

Du, Huiwen; Li, Denghua; Wang, Yibing; Wang, Chenxuan; Zhang, Dongdong; Yang, Yan-lian; Wang, Chen

2013-08-29

We report here the measurement of the temperature-dependent surface charge density of purple membrane (PM) by using electrostatic force microscopy (EFM). The surface charge density was measured to be 3.4 × 10(5) e/cm(2) at room temperature and reaches the minimum at around 52 °C. The initial decrease of the surface charge density could be attributed to the reduced dipole alignment because of the thermally induced protein mobility in PM. The increase of charge density at higher temperature could be ascribed to the weakened interaction between proteins and the lipids, which leads to the exposure of the charged amino acids. This work could be a benefit to the direct assessment of the structural stability and electric properties of biological membranes at the nanoscale.

Experimental and computational studies on the electronic excited states of nitrobenzene

NASA Astrophysics Data System (ADS)

Krishnakumar, Sunanda; Das, Asim Kumar; Singh, Param Jeet; Shastri, Aparna; Rajasekhar, B. N.

2016-11-01

The gas phase electronic absorption spectrum of nitrobenzene (C6H5NO2) in the 4.5-11.2 eV region is recorded using synchrotron radiation with a view to comprehend the nature of the excited states. Electronic excited states of nitrobenzene are mainly classified as local excitations within the benzene ring or nitro group and charge transfer excitations between the benzene and nitro group, with some transitions showing percentage from both. The nature of molecular orbitals, their orderings and energies are obtained from density functional theory calculations which help in assigning partially assigned/unassigned features in earlier photoelectron spectroscopy studies. Optimized geometry of ionic nitrobenzene predicts redistribution of charge density in the benzene ring rather than the nitro group resulting in stabilization of the benzene ring π orbitals in comparison to the neutral molecule. Time dependent density functional theory computations are found to describe the experimental spectra well with respect to energies, relative intensities and nature of the observed transitions in terms of valence, Rydberg or charge transfer type. New insights into the interpretation of 1B2u←1A1g and 1B1u←1A1g shifted benzene transitions in light of the present computational calculations are presented. The first few members of the ns, np and nd type Rydberg series in nitrobenzene, converging to the first six ionization potentials, identified in the spectra as weak but sharp peaks are reported for the first time. In general, transitions to the lowest three unoccupied molecular orbitals 4b1, 3a2 and 5b1 are valence or charge transfer in nature, while excitations to higher orbitals are predominantly Rydberg in nature. This work presents a consolidated experimental study and theoretical interpretation of the electronic absorption spectrum of nitrobenzene.

Ultrafast semi-metallic layer formation in detonating nitromethane

NASA Astrophysics Data System (ADS)

Reed, Evan; Manaa, M. Riad; Fried, Laurence; Glaesemann, Kurt; Joannopoulos, John

2008-03-01

We present the first quantum molecular dynamics simulations behind a detonation front (up to 0.2 ns) of the explosive nitromethane (CH3NO2) represented by the density-functional-based tight-binding method (DFTB). This simulation is enabled by our recently developed multi-scale shock wave molecular dynamics technique (MSST) that opens the door to longer duration simulations by several orders of magnitude. The electronic density of states around the Fermi energy initially increases as metastable material states are produced but then later decreases, perhaps unexpectedly. These changes indicate that the shock front is characterized by an increase in optical thickness and conductivity followed by a reduction around 100 picoseconds behind the front. We find that a significant population of intermediate metastable molecules are charged and charged species play an important role in the density of states evolution. The transient transformation to a semi-metallic state can be understood within the Anderson picture of metallization.

Communication: Charge-population based dispersion interactions for molecules and materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stöhr, Martin; Department Chemie, Technische Universität München, Lichtenbergstr. 4, D-85748 Garching; Michelitsch, Georg S.

2016-04-21

We introduce a system-independent method to derive effective atomic C{sub 6} coefficients and polarizabilities in molecules and materials purely from charge population analysis. This enables the use of dispersion-correction schemes in electronic structure calculations without recourse to electron-density partitioning schemes and expands their applicability to semi-empirical methods and tight-binding Hamiltonians. We show that the accuracy of our method is en par with established electron-density partitioning based approaches in describing intermolecular C{sub 6} coefficients as well as dispersion energies of weakly bound molecular dimers, organic crystals, and supramolecular complexes. We showcase the utility of our approach by incorporation of the recentlymore » developed many-body dispersion method [Tkatchenko et al., Phys. Rev. Lett. 108, 236402 (2012)] into the semi-empirical density functional tight-binding method and propose the latter as a viable technique to study hybrid organic-inorganic interfaces.« less

Flocculation of Clay Colloids Induced by Model Polyelectrolytes: Effects of Relative Charge Density and Size.

PubMed

Sakhawoth, Yasine; Michot, Laurent J; Levitz, Pierre; Malikova, Natalie

2017-10-06

Flocculation and its tuning are of utmost importance in the optimization of several industrial protocols in areas such as purification of waste water and civil engineering. Herein, we studied the polyelectrolyte-induced flocculation of clay colloids on a model system consisting of purified clay colloids of well-defined size fractions and ionene polyelectrolytes presenting regular and tunable chain charge density. To characterize ionene-induced clay flocculation, we turned to the combination of light absorbance (turbidity) and ζ-potential measurements, as well as adsorption isotherms. Our model system allowed us to identify the exact ratio of positive and negative charges in clay-ionene mixtures, the (c+/c-) ratio. For all samples studied, the onset of efficient flocculation occurred consistently at c+/c- ratios significantly below 1, which indicated the formation of highly ionene-deficient aggregates. At the same time, the ζ-potential measurements indicated an apparent zero charge on such aggregates. Thus, the ζ-potential values could not provide the stoichiometry inside the clay-ionene aggregates. The early onset of flocculation in clay-ionene mixtures is reminiscent of the behavior of multivalent salts and contrasts that of monovalent salts, for which a large excess amount of ions is necessary to achieve flocculation. Clear differences in the flocculation behavior are visible as a function of the ionene charge density, which governs the conformation of the ionene chains on the clay surface. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Density functional study of the electronic structure of dye-functionalized fullerenes and their model donor-acceptor complexes containing P3HT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baruah, Tunna; Garnica, Amanda; Paggen, Marina

2016-04-14

We study the electronic structure of C{sub 60} fullerenes functionalized with a thiophene-diketo-pyrrolopyrrole-thiophene based chromophore using density functional theory combined with large polarized basis sets. As the attached chromophore has electron donor character, the functionalization of the fullerene leads to a donor-acceptor (DA) system. We examine in detail the effect of the linker and the addition site on the electronic structure of the functionalized fullerenes. We further study the electronic structure of these DA complexes with a focus on the charge transfer excitations. Finally, we examine the interface of the functionalized fullerenes with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor. Ourmore » results show that all functionalized fullerenes with an exception of the C{sub 60}-pyrrolidine [6,6], where the pyrrolidine is attached at a [6,6] site, have larger electron affinities relative to the pristine C{sub 60} fullerene. We also estimate the quasi-particle gap, lowest charge transfer excitation energy, and the exciton binding energies of the functionalized fullerene-P3MT model systems. Results show that the exciton binding energies in these model complexes are slightly smaller compared to a similarly prepared phenyl-C{sub 61}-butyric acid methyl ester (PCBM)-P3MT complex.« less

Detailed solvent, structural, quantum chemical study and antimicrobial activity of isatin Schiff base

NASA Astrophysics Data System (ADS)

Brkić, Dominik R.; Božić, Aleksandra R.; Marinković, Aleksandar D.; Milčić, Miloš K.; Prlainović, Nevena Ž.; Assaleh, Fathi H.; Cvijetić, Ilija N.; Nikolić, Jasmina B.; Drmanić, Saša Ž.

2018-05-01

The ratios of E/Z isomers of sixteen synthesized 1,3-dihydro-3-(substituted phenylimino)-2H-indol-2-one were studied using experimental and theoretical methodology. Linear solvation energy relationships (LSER) rationalized solvent influence of the solvent-solute interactions on the UV-Vis absorption maxima shifts (νmax) of both geometrical isomers using the Kamlet-Taft equation. Linear free energy relationships (LFER) in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on pKa, NMR chemical shifts and νmax values. Electron charge density was obtained by the use of Quantum Theory of Atoms in Molecules, i.e. Bader's analysis. The substituent and solvent effect on intramolecular charge transfer (ICT) were interpreted with the aid of time-dependent density functional (TD-DFT) method. Additionally, the results of TD-DFT calculations quantified the efficiency of ICT from the calculated charge-transfer distance (DCT) and amount of transferred charge (QCT). The antimicrobial activity was evaluated using broth microdilution method. 3D QSAR modeling was used to demonstrate the influence of substituents effect as well as molecule geometry on antimicrobial activity.

Helium escape from the Earth's atmosphere - The charge exchange mechanism revisited

NASA Technical Reports Server (NTRS)

Lie-Svendsen, O.; Rees, M. H.; Stamnes, K.

1992-01-01

We have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.

Space and surface charge behavior analysis of charge-eliminated polymer films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oda, Tetsuji; Takashima, Kazunori; Ichiyama, Shinichiro

1995-12-31

Charge behavior of corona-charged or charge eliminated polymer films being dipped in the city water were studied. They were polytetrafluoroethylene (PTFE teflon{trademark}), polypropylene (PP), low density or high density polyethylene (LDPE or HDPE) thin films which are as grown (native) or plasma-processed. The plasma processing at low pressure was tested as antistatic processing. Charge elimination was done by being dipped in alcohol or city water. TSDC analysis and surface charge profile measurement were done for both charged and charge eliminated polymer films. Surface charge density of plasma processed polymer films just after corona charging is roughly the same as thatmore » of an original film. There is little difference between surface charge density profile of a native film and that of a plasma processed film. A large hetero current peak of TSDC was observed at room temperature for a processed film. It was found that the hetero peak disappears after charge elimination process. A pressure pulse wave method by using a pulse-driven piezoelectric PVDF polymer film as a piezoelectric actuator was newly developed to observe real space charge distribution. A little difference of internal space charge distribution between the plasma processed film and the native one after corona charging is found.« less

(LaTiO3)n/(LaVO3)n as a model system for unconventional charge transfer and polar metallicity

NASA Astrophysics Data System (ADS)

Weng, Yakui; Zhang, Jun-Jie; Gao, Bin; Dong, Shuai

At interfaces between oxide materials, lattice and electronic reconstructions always play important roles in exotic phenomena. In this study, the density-functional theory and maximally localized Wannier functions are employed to investigate the (LaTiO3)n/(LaVO3)n magnetic superlattices. By considering lattice distortion and dimensional effect, many interesting interfacial physics have been found in the n = 1 superlattice, e.g. magnetic phase transition, unconventional charge transfer, and metal-insulator transition. In addition, the compatibility among the polar structure, ferrimagnetism, and metallicity is predicted in the n = 2 superlattice.

Structure and stability of complexes of agmatine with some functional receptor residues of proteins

NASA Astrophysics Data System (ADS)

Remko, Milan; Broer, Ria; Remková, Anna; Van Duijnen, Piet Th.

2017-04-01

The paper reports the results of a theoretical study of the conformational behavior and basicity of biogenic amine agmatine. The complexes modelling of agmatine - protein interaction are also under scrutiny of our investigation using the Becke3LYP and B97D levels of the density functional theory. The relative stabilities (Gibbs energies) of individual complexes are by both DFT methods described equally. Hydration has a dramatic effect on the hydrogen bonded complexes studied. The pairing acidic carboxylate group with different agmatine species resulted in charged hydrogen bond complexes containing negatively charged acetate species acting as proton acceptors.

Magnetic anisotropy of metal functionalized phthalocyanine 2D networks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Guojun; Zhang, Yun; Xiao, Huaping, E-mail: hpxiao@xtu.edu.cn

2016-06-15

The magnetic anisotropy of metal including Cr, Mn, Fe, Co, Mo, Tc, Ru, Rh, W, Re, Os, Ir atoms functionalized phthalocyanine networks have been investigated with first-principles calculations. The magnetic moments can be expressed as 8-n μ{sub B} with n the electronic number of outmost d shell in the transition metals. The huge magnetocrystalline anisotropy energy (MAE) is obtained by torque method. Especially, the MAE of Re functionalized phthalocyanine network is about 20 meV with an easy axis perpendicular to the plane of phthalocyanine network. The MAE is further manipulated by applying the external biaxial strain. It is found thatmore » the MAE is linear increasing with the external strain in the range of −2% to 2%. Our results indicate an effective approach to modulate the MAE for practical application. - Graphical abstract: The charge density redistribution (ρ{sub MPc}-ρ{sub M}-ρ{sub Pc}) and spin density of the CoPc molecule, from top- and side-views. Purple and green isosurfaces indicate charge depletion and accumulation, respectively. Display Omitted.« less

Electrical Transfer Function and Poling Mechanisms for Nonlinear Optical Polymer Modulators

NASA Technical Reports Server (NTRS)

Watson, Michael Dale

2004-01-01

Electro-Optic Polymers hold great promise in increased electro-optic coefficients as compared to their inorganic corollaries. Many researchers have focused on quantum chemistry to describe how the dipoles respond to temperature and electric fields. Much work has also been done for single layer films to confirm these results. For optical applications, waveguide structures are utilized to guide the optical waves in 3 layer stacks. Electrode poling is the only practical poling method for these structures. This research takes an electrical engineering approach to develop poling models and electrical and optical transfer functions of the waveguide structure. The key aspect of the poling model is the large boundary charge density deposited during the poling process. The boundary charge density also has a large effect on the electrical transfer function which is used to explain the transient response of the system. These models are experimentally verified. Exploratory experiment design is used to study poling parameters including time, temperature, and voltage. These studies verify the poling conditions for CLDX/APC and CLDZ/APEC guest host electro optic polymer films in waveguide stacks predicted by the theoretical developments.

Quantum Monte Carlo analysis of a charge ordered insulating antiferromagnet: The Ti 4O 7 Magneli phase

DOE PAGES

Benali, Anouar; Shulenburger, Luke; Krogel, Jaron T.; ...

2016-06-07

The Magneli phase Ti 4O 7 is an important transition metal oxide with a wide range of applications because of its interplay between charge, spin, and lattice degrees of freedom. At low temperatures, it has non-trivial magnetic states very close in energy, driven by electronic exchange and correlation interactions. We have examined three low- lying states, one ferromagnetic and two antiferromagnetic, and calculated their energies as well as Ti spin moment distributions using highly accurate Quantum Monte Carlo methods. We compare our results to those obtained from density functional theory- based methods that include approximate corrections for exchange and correlation.more » Our results confirm the nature of the states and their ordering in energy, as compared with density-functional theory methods. However, the energy differences and spin distributions differ. Here, a detailed analysis suggests that non-local exchange-correlation functionals, in addition to other approximations such as LDA+U to account for correlations, are needed to simultaneously obtain better estimates for spin moments, distributions, energy differences and energy gaps.« less

The Optoelectronic Properties of Nanoparticles from First Principles Calculations

NASA Astrophysics Data System (ADS)

Brawand, Nicholas Peter

The tunable optoelectronic properties of nanoparticles through the modification of their size, shape, and surface chemistry, make them promising platforms for numerous applications, including electronic and solar conversion devices. However, the rational design and optimization of nanostructured materials remain open challenges, e.g. due to difficulties in controlling and reproducing synthetic processes and in precise atomic-scale characterization. Hence, the need for accurate theoretical predictions, which can complement and help interpret experiments and provide insight into the underlying physical properties of nanostructured materials. This dissertation focuses on the development and application of first principles calculations to predict the optoelectronic properties of nanoparticles. Novel methods based on density functional theory are developed, implemented, and applied to predict both optical and charge transport properties. In particular, the generalization of dielectric dependent hybrid functionals to finite systems is introduced and shown to yield highly accurate electronic structure properties of molecules and nanoparticles, including photoemission and absorption properties. In addition, an implementation of constrained density functional theory is discussed, for the calculation of hopping transport in nanoparticle systems. The implementation was verified against literature results and compared against other methods used to compute transport properties, showing that some methods used in the literature give unphysical results for thermally disordered systems. Furthermore, the constrained density functional theory implementation was coupled to the self-consistent image charge method, making it possible to include image charge effects self-consistently when predicting charge transport properties of nanoparticles near interfaces. The methods developed in this dissertation were then applied to study the optoelectronic and transport properties of specific systems, in particular, silicon and lead chalcogenide nanoparticles. In the case of Si, blinking in oxidized Si nanoparticles was addressed. Si dangling bonds at the surface were found to introduce defect states which, depending on their charge and local stress conditions, may give rise to ON and OFF states responsible for exponential blinking statistics. We also investigated, engineering of band edge positions of nanoparticles through post-synthetic surface chemistry modification, with a focus on lead chalcogenides. In collaboration with experiment, we demonstrated how band edge positions of lead sulfide nanoparticles can be tuned by over 2.0 eV. We established a clear relationship between ligand dipole moments and nanoparticle band edge shifts which can be used to engineer nanoparticles for optoelectronic applications. Calculations of transport properties focused on charge transfer in silicon and lead chalcogenide nanoparticles. Si nanoparticles with deep defects and shallow impurities were investigated, showing that shallow defects may be more detrimental to charge transport than previously assumed. In the case of lead chalcogenide nanoparticles, hydrogen was found to form complexes with defects which can be used to remove potentially detrimental charge traps in nanoparticle solids. The methods and results presented in this dissertation are expected to help guide engineering of nanoparticles for future device applications.

Effect of surface charge density on the affinity of oxide nanoparticles for the vapor-water interface.

PubMed

Brown, Matthew A; Duyckaerts, Nicolas; Redondo, Amaia Beloqui; Jordan, Inga; Nolting, Frithjof; Kleibert, Armin; Ammann, Markus; Wörner, Hans Jakob; van Bokhoven, Jeroen A; Abbas, Zareen

2013-04-23

Using in-situ X-ray photoelectron spectroscopy at the vapor-water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye-Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si-O(-)) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor-water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye-Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.

Revealing hidden antiferromagnetic correlations in doped Hubbard chains via string correlators

NASA Astrophysics Data System (ADS)

Hilker, Timon A.; Salomon, Guillaume; Grusdt, Fabian; Omran, Ahmed; Boll, Martin; Demler, Eugene; Bloch, Immanuel; Gross, Christian

2017-08-01

Topological phases, like the Haldane phase in spin-1 chains, defy characterization through local order parameters. Instead, nonlocal string order parameters can be employed to reveal their hidden order. Similar diluted magnetic correlations appear in doped one-dimensional lattice systems owing to the phenomenon of spin-charge separation. Here we report on the direct observation of such hidden magnetic correlations via quantum gas microscopy of hole-doped ultracold Fermi-Hubbard chains. The measurement of nonlocal spin-density correlation functions reveals a hidden finite-range antiferromagnetic order, a direct consequence of spin-charge separation. Our technique, which measures nonlocal order directly, can be readily extended to higher dimensions to study the complex interplay between magnetic order and density fluctuations.

The Self-Association of Graphane Is Driven by London Dispersion and Enhanced Orbital Interactions.

PubMed

Wang, Changwei; Mo, Yirong; Wagner, J Philipp; Schreiner, Peter R; Jemmis, Eluvathingal D; Danovich, David; Shaik, Sason

2015-04-14

We investigated the nature of the cohesive energy between graphane sheets via multiple CH···HC interactions, using density functional theory (DFT) including dispersion correction (Grimme's D3 approach) computations of [n]graphane σ dimers (n = 6-73). For comparison, we also evaluated the binding between graphene sheets that display prototypical π/π interactions. The results were analyzed using the block-localized wave function (BLW) method, which is a variant of ab initio valence bond (VB) theory. BLW interprets the intermolecular interactions in terms of frozen interaction energy (ΔE(F)) composed of electrostatic and Pauli repulsion interactions, polarization (ΔE(pol)), charge-transfer interaction (ΔE(CT)), and dispersion effects (ΔE(disp)). The BLW analysis reveals that the cohesive energy between graphane sheets is dominated by two stabilizing effects, namely intermolecular London dispersion and two-way charge transfer energy due to the σ(CH) → σ*(HC) interactions. The shift of the electron density around the nonpolar covalent C-H bonds involved in the intermolecular interaction decreases the C-H bond lengths uniformly by 0.001 Å. The ΔE(CT) term, which accounts for ∼15% of the total binding energy, results in the accumulation of electron density in the interface area between two layers. This accumulated electron density thus acts as an electronic "glue" for the graphane layers and constitutes an important driving force in the self-association and stability of graphane under ambient conditions. Similarly, the "double faced adhesive tape" style of charge transfer interactions was also observed among graphene sheets in which it accounts for ∼18% of the total binding energy. The binding energy between graphane sheets is additive and can be expressed as a sum of CH···HC interactions, or as a function of the number of C-H bonds.

Relating saturation capacity to charge density in strong cation exchangers.

PubMed

Steinebach, Fabian; Coquebert de Neuville, Bertrand; Morbidelli, Massimo

2017-07-21

In this work the relation between physical and chemical resin characteristics and the total amount of adsorbed protein (saturation capacity) for ion-exchange resins is discussed. Eleven different packing materials with a sulfo-functionalization and one multimodal resin were analyzed in terms of their porosity, pore size distribution, ligand density and binding capacity. By specifying the ligand density and binding capacity by the total and accessible surface area, two different groups of resins were identified: Below a ligand density of approx. 2.5μmol/m 2 area the ligand density controls the saturation capacity, while above this limit the accessible surface area becomes the limiting factor. This results in a maximum protein uptake of around 2.5mg/m 2 of accessible surface area. The obtained results allow estimating the saturation capacity from independent resin characteristics like the saturation capacity mainly depends on "library data" such as the accessible and total surface area and the charge density. Hence these results give an insight into the fundamentals of protein adsorption and help to find suitable resins, thus limiting the experimental effort in early process development stages. Copyright © 2017 Elsevier B.V. All rights reserved.

Density of states, optical and thermoelectric properties of perovskite vanadium fluorides Na3VF6

NASA Astrophysics Data System (ADS)

Reshak, A. H.; Azam, Sikander

2014-05-01

The electronic structure, charge density and Fermi surface of Na3VF6 compound have been examined with the support of density functional theory (DFT). Using the full potential linear augmented plane wave method, we employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel-Vosko GGA (EVGGA) to treat the exchange correlation potential to solve Kohn-Sham equations. The calculation show that Na3VF6 compound has metallic nature and the Fermi energy (EF) is assessed by overlapping of V-d state. The calculated density of states at the EF are about 18.655, 51.932 and 13.235 states/eV, and the bare linear low-temperature electronic specific heat coefficient (γ) is found to be 3.236 mJ/mol-K2, 9.008 mJ/mol-K2 and 2.295 mJ/mol-K2 for LDA, GGA and EVGGA, respectively. The Fermi surface is composed of two sheets. The chemical bonding of Na3VF6 compound is analyzed through the electronic charge density in the (1 1 0) crystallographic plane. The optical constants and thermal properties were also calculated and discussed.

The electronic and optical properties of Cs adsorbed GaAs nanowires via first-principles study

NASA Astrophysics Data System (ADS)

Diao, Yu; Liu, Lei; Xia, Sihao; Feng, Shu; Lu, Feifei

2018-07-01

In this study, we investigate the Cs adsorption mechanism on (110) surface of zinc-blende GaAs nanowire. The adsorption energy, work function, dipole moment, geometric structure, Mulliken charge distribution, charge transfer index, band structures, density of state and optical properties of Cs adsorption structures are calculated utilizing first-principles method based on density function theory. Total-energy calculations show that all the adsorption energies are negative, indicating that Cs adsorption process is exothermic and Cs covered GaAs nanowires are stable. The work function of nanowire surface has an obvious decrease after Cs adsorption. Besides, the ionization of nanowire surface is enhanced as well. More importantly, Cs adsorption contributes to a lower side shift of bands near Fermi level, and the corresponding band gap disappears. Additionally, the absorption peak and energy loss function after Cs adsorption are far higher than those before adsorption, implying better light absorption characteristic of nanowire surface after Cs adsorption. These theoretical calculations can directly guide the Cs activation experiment for negative electron affinity GaAs nanowire, and also lay a foundation for the further study of Cs/O co-adsorption on the nanowire surface.

First-Principles Molecular Dynamics Simulations of NaCl in Water: Performance of Advanced Exchange-Correlation Approximations in Density Functional Theory

NASA Astrophysics Data System (ADS)

Yao, Yi; Kanai, Yosuke

Our ability to correctly model the association of oppositely charged ions in water is fundamental in physical chemistry and essential to various technological and biological applications of molecular dynamics (MD) simulations. MD simulations using classical force fields often show strong clustering of NaCl in the aqueous ionic solutions as a consequence of a deep contact pair minimum in the potential of mean force (PMF) curve. First-Principles Molecular Dynamics (FPMD) based on Density functional theory (DFT) with the popular PBE exchange-correlation approximation, on the other hand, show a different result with a shallow contact pair minimum in the PMF. We employed two of most promising exchange-correlation approximations, ωB97xv by Mardiorossian and Head-Gordon and SCAN by Sun, Ruzsinszky and Perdew, to examine the PMF using FPMD simulations. ωB97xv is highly empirically and optimized in the space of range-separated hybrid functional with a dispersion correction while SCAN is the most recent meta-GGA functional that is constructed by satisfying various known conditions in well-defined physical limits. We will discuss our findings for PMF, charge transfer, water dipoles, etc.

Friedel oscillation near a van Hove singularity in two-dimensional Dirac materials

NASA Astrophysics Data System (ADS)

Lu, Chi-Ken

2016-02-01

We consider Friedel oscillation in the two-dimensional Dirac materials when the Fermi level is near the van Hove singularity. Twisted graphene bilayer and the surface state of topological crystalline insulator are the representative materials which show low-energy saddle points that are feasible to probe by gating. We approximate the Fermi surface near saddle point with a hyperbola and calculate the static Lindhard response function. Employing a theorem of Lighthill, the induced charge density δ n due to an impurity is obtained and the algebraic decay of δ n is determined by the singularity of the static response function. Although a hyperbolic Fermi surface is rather different from a circular one, the static Lindhard response function in the present case shows a singularity similar with the response function associated with circular Fermi surface, which leads to the δ n\\propto {{R}-2} at large distance R. The dependences of charge density on the Fermi energy are different. Consequently, it is possible to observe in twisted graphene bilayer the evolution that δ n\\propto {{R}-3} near Dirac point changes to δ n\\propto {{R}-2} above the saddle point. Measurements using scanning tunnelling microscopy around the impurity sites could verify the prediction.

Density functional theory based probe of the affinity interaction of saccharide ligands with extra-cellular sialic acid residues.

PubMed

Patel, Anjali; Tiwari, Sanjay; Jha, Prafulla K

2018-05-10

Changes in glycosylation pattern leads to malignant transformations among the cells. In combination with upregulated actions of sialyltransferases, it ultimately leads to differential expression of sialic acid (SA) at cell surface. Given its negative charge and localization to extracellular domain, SA has been exploited for the development of targeted theranostics using approaches, such as, cationization and appending recognition saccharides on carrier surface. In this study, we have performed quantum mechanical calculations based on density functional theory (DFT) to study the interaction of saccharides with extracellular SA. Gradient-corrected DFT with the three parameter function (B3) was utilized for the calculation of Lee-Yang-Parr (LYP) correlation function. Atomic charge, vibrational frequencies and energy of the optimized structures were calculated through B3LYP. Our calculations demonstrate a stronger galactose-sialic acid interaction at tumour-relevant low pH and hyperthermic condition. These results support the application of pH responsive delivery vehicles and targeted hyperthermic chemotherapy for eradicating solid tumour deposits. These studies, conducted a priori, can guide the formulation scientists over appropriate choice of ligands and their applications in the design of 'smart' theranostic tools.

On contribution of known atomic partial charges of protein backbone in electrostatic potential density maps

PubMed Central

2017-01-01

Abstract Partial charges of atoms in a molecule and electrostatic potential (ESP) density for that molecule are known to bear a strong correlation. In order to generate a set of point‐field force field parameters for molecular dynamics, Kollman and coworkers have extracted atomic partial charges for each of all 20 amino acids using restrained partial charge‐fitting procedures from theoretical ESP density obtained from condensed‐state quantum mechanics. The magnitude of atomic partial charges for neutral peptide backbone they have obtained is similar to that of partial atomic charges for ionized carboxylate side chain atoms. In this study, the effect of these known atomic partial charges on ESP is examined using computer simulations and compared with the experimental ESP density recently obtained for proteins using electron microscopy. It is found that the observed ESP density maps are most consistent with the simulations that include atomic partial charges of protein backbone. Therefore, atomic partial charges are integral part of atomic properties in protein molecules and should be included in model refinement. PMID:28370507

Underscreening in ionic liquids: a first principles analysis.

PubMed

Rotenberg, Benjamin; Bernard, Olivier; Hansen, Jean-Pierre

2018-02-07

An attempt is made to understand the underscreening effect, observed in concentrated electrolyte solutions or melts, on the basis of simple, admittedly crude models involving charged (for the ions) and neutral (for the solvent molecules) hard spheres. The thermodynamic and structural properties of these 'primitive' and 'semi-primitive' models are calculated within mean spherical approximation, which provides the basic input required to determine the partial density response functions. The screening length [Formula: see text], which is unambiguously defined in terms of the wave-number-dependent response functions, exhibits a cross-over from a low density, Debye-like regime, to a regime where [Formula: see text] increases with density beyond a critical density at which the Debye length [Formula: see text] becomes comparable to the ion diameter. In this high density regime the ratio [Formula: see text] increases according to a power law, in qualitative agreement with experimental measurements, albeit at a much slower rate.

Underscreening in ionic liquids: a first principles analysis

NASA Astrophysics Data System (ADS)

Rotenberg, Benjamin; Bernard, Olivier; Hansen, Jean-Pierre

2018-02-01

An attempt is made to understand the underscreening effect, observed in concentrated electrolyte solutions or melts, on the basis of simple, admittedly crude models involving charged (for the ions) and neutral (for the solvent molecules) hard spheres. The thermodynamic and structural properties of these ‘primitive’ and ‘semi-primitive’ models are calculated within mean spherical approximation, which provides the basic input required to determine the partial density response functions. The screening length λS , which is unambiguously defined in terms of the wave-number-dependent response functions, exhibits a cross-over from a low density, Debye-like regime, to a regime where λS increases with density beyond a critical density at which the Debye length λD becomes comparable to the ion diameter. In this high density regime the ratio λ_S/λD increases according to a power law, in qualitative agreement with experimental measurements, albeit at a much slower rate.

First-row diatomics: Calculation of the geometry and energetics using self-consistent gradient-functional approximations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kutzler, F.W.; Painter, G.S.

1992-02-15

A fully self-consistent series of nonlocal (gradient) density-functional calculations has been carried out using the augmented-Gaussian-orbital method to determine the magnitude of gradient corrections to the potential-energy curves of the first-row diatomics, Li{sub 2} through F{sub 2}. Both the Langreth-Mehl-Hu and the Perdew-Wang gradient-density functionals were used in calculations of the binding energy, bond length, and vibrational frequency for each dimer. Comparison with results obtained in the local-spin-density approximation (LSDA) using the Vosko-Wilk-Nusair functional, and with experiment, reveals that bond lengths and vibrational frequencies are rather insensitive to details of the gradient functionals, including self-consistency effects, but the gradient correctionsmore » reduce the overbinding commonly observed in the LSDA calculations of first-row diatomics (with the exception of Li{sub 2}, the gradient-functional binding-energy error is only 50--12 % of the LSDA error). The improved binding energies result from a large differential energy lowering, which occurs in open-shell atoms relative to the diatomics. The stabilization of the atom arises from the use of nonspherical charge and spin densities in the gradient-functional calculations. This stabilization is negligibly small in LSDA calculations performed with nonspherical densities.« less

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory.

PubMed

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G

2011-08-28

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi-Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi-Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. © 2011 American Institute of Physics

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

PubMed Central

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

2011-01-01

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi–Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi–Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. PMID:21895159

Effective Electrostatic Interactions Between Two Overall Neutral Surfaces with Quenched Charge Heterogeneity Over Atomic Length Scale

NASA Astrophysics Data System (ADS)

Zhou, S.

2017-12-01

Using Monte Carlo results as a reference, a classical density functional theory ( CDFT) is shown to reliably predict the forces between two heterogeneously charged surfaces immersed in an electrolyte solution, whereas the Poisson-Boltzmann ( PB) theory is demonstrated to deteriorate obviously for the same system even if the system parameters considered fall within the validity range of the PB theory in the homogeneously charged surfaces. By applying the tested CDFT, we study the effective electrostatic potential of mean force ( EPMF) between two face-face planar and hard surfaces of zero net charge on which positive and negative charges are separated and considered to present as discontinuous spots on the inside edges of the two surfaces. Main conclusions are summarized as follows: (i) strength of the EPMF in the surface charge separation case is very sensitively and positively correlated with the surface charge separation level and valency of the salt ion. Particularly, the charge separation level and the salt ion valency have a synergistic effect, which makes high limit of the EPMF strength in the surface charge separation case significantly go beyond that of the ideal homogeneously charged surface counterpart at average surface charge density similar to the average surface positive or negative charge density in the charge separation case. (ii) The surface charge distribution patterns mainly influence sign of the EPMF: symmetrical and asymmetrical patterns induce repulsive and attractive (at small distances) EPMF, respectively; but with low valency salt ions and low charge separation level the opposite may be the case. With simultaneous presence of both higher valency cation and anion, the EPMF can be repulsive at intermediate distances for asymmetrical patterns. (iii) Salt ion size has a significant impact, which makes the EPMF tend to become more and more repulsive with the ion diameter regardless of the surface charge distribution patterns and the valency of the salt ion; whereas if the 1:1 type electrolyte and the symmetrical patterns are considered, then the opposite may be the case. All of these findings can be explained self-consistently from several perspectives: an excess adsorption of the salt ions (induced by the surface charge separation) serving to raise the osmotic pressure between the plates, configuration fine-tuning in the thinner ion adsorption layer driven by the energy decrease principle, direct Coulombic interactions operating between charged objects on the two face-to-face plates involved, and net charge strength in the ion adsorption layer responsible for the net electrostatic repulsion.

Crystallographic perturbations to valence charge density and hydrogen-surface interactions

NASA Astrophysics Data System (ADS)

Ciston, James W.

The subject of surfaces has been the epicenter of numerous studies in recent years, particularly with respect to applications in catalysis, thin films, and self-assembly of nanostructures where the surface-to-volume ratio is large. Understanding how the atomic structure of materials differs at surfaces where the atoms are far less constrained can yield fundamental insight into these interesting nanoscale phenomena. Quantum surface crystallography takes this one step further in an attempt to experimentally measure the structure of the electrons themselves, which is of greater importance than atomic positions in determining material properties. We report a procedure for obtaining a much better initial parameterization of the charge density than what is possible from a neutral atom model. This procedure involves the parameterization of a bulk charge density model in terms of simple variables such as bond lengths, which can then be transferred to the problem of interest, for instance a surface. Parameterization is accomplished through the fitting of Density Functional Theory calculations of a variety of crystal distortions to a bond-centered pseudoatom (BCPA) model. This parameterized model can then be applied to surfaces or for other problems where an initial higher-order model is needed without the addition of any extra fitted parameters. Through the use of the BCPA model, we report a three-dimensional charge density refinement from x-ray diffraction intensities of the Si (001) 2x1H surface. By properly accounting for the covalent bonding effects in the silicon structure, we were able to stably refine the positions of hydrogen atoms at this surface in three dimensions, which had never before been accomplished for any surface. In addition, we found experimentally an increased, slightly localized bond density of approximately 0.31 electrons between each Si atom pair at the surface. Both the atomic positions and the charge density were found to be in remarkably good agreement with density functional theory (DFT) calculations. The BCPA model was also applied to an experimental refinement of the local charge density at the Si (111) 7x7 surface utilizing a combination of x-ray and high energy electron diffraction. By perturbing about the bond-centered pseudoatom model, we found experimentally that the adatoms were in an anti-bonding state with the atoms directly below. We were also able to experimentally refine a charge transfer of 0.26+/-0.04 e- from each adatom site to the underlying layers. This was the first statistically significant refinement of site-specific bonding information at any surface utilizing x-ray diffraction data. Precession electron diffraction (PED) is a technique which is gaining increasing interest due to its ease of use and reduction of the dynamical scattering problem in electron diffraction. To further investigate the usefulness of this technique, we performed a systematic study of the effect of precession angle on the mineral andalusite where the semiangle was varied from 6.5 to 32 mrad in five discrete steps. We have shown that the intensities of kinematically forbidden reflections decayed exponentially as the precession semiangle (ϕ) was increased. Additionally, we have determined that charge density effects were best observed at moderately low angles (6.5-13 mrad) even though PED patterns became more kinematical in nature as the precession angle was increased further. We have also shown that the amount of interpretable information provided by direct methods phase inversion of the diffraction data increases monotonically but non-systematically as ϕ increases. We report an experimental and theoretical analysis of the ✓3x✓3-R30° and 2x2 reconstructions on the MgO (111) surface combining transmission electron microscopy, x-ray photoelectron spectroscopy, and reasonably accurate density functional calculations using the meta-GGA functional TPSS. We have not only conclusively solved the atomic structures of these reconstructions, but have developed a kinetic model for an evolutionary pathway between structures driven entirely by exchange of water molecules between the surface and the environment that does not require the cations to move when the structure transforms. This is the first time an experimentally and theoretically supported kinetic model has described not only all of the structures in a series on a single oxide surface, but also describes why none of the structures pass through the thermodynamically most stable configuration. Lastly, we have investigated the observability of valence bonding effects in aberration-corrected high resolution electron microscopy (HREM) images along the [010] projection of the mineral Forsterite (Mg2SiO 4). Direct observability of bonding effects would be both faster and less ambiguous than the refinement of similar features against diffraction data. Through analysis of simulated high resolution electron microscopy images, we have determined that bonding effects should be observable at levels approaching 20% of the total contrast. Initial experimental results for this material system have also been presented.

Interfacial dynamic surface traps of lead sulfide (PbS) nanocrystals: test-platform for interfacial charge carrier traps at the organic/inorganic functional interface

NASA Astrophysics Data System (ADS)

Kim, Youngjun; Ko, Hyungduk; Park, Byoungnam

2018-04-01

Nanocrystal (NC) size and ligand dependent dynamic trap formation of lead sulfide (PbS) NCs in contact with an organic semiconductor were investigated using a pentacene/PbS field effect transistor (FET). We used a bilayer pentacene/PbS FET to extract information of the surface traps of PbS NCs at the pentacene/PbS interface through the field effect-induced charge carrier density measurement in the threshold and subthreshold regions. PbS size and ligand dependent trap properties were elucidated by the time domain and threshold voltage measurements in which threshold voltage shift occurs by carrier charging and discharging in the trap states of PbS NCs. The observed threshold voltage shift is interpreted in context of electron trapping through dynamic trap formation associated with PbS NCs. To the best of our knowledge, this is the first demonstration of the presence of interfacial dynamic trap density of PbS NC in contact with an organic semiconductor (pentacene). We found that the dynamic trap density of the PbS NC is size dependent and the carrier residence time in the specific trap sites is more sensitive to NC size variation than to NC ligand exchange. The probing method presented in the study offers a means to investigate the interfacial surface traps at the organic-inorganic hetero-junction, otherwise understanding of the buried surface traps at the functional interface would be elusive.

Microscopic coexistence of magnetism and superconductivity in charge-compensated Ba1-xKx(Fe1-yCoy)2As2

NASA Astrophysics Data System (ADS)

Goltz, Til; Zinth, Veronika; Johrendt, Dirk; Rosner, Helge; Pascua, Gwendolyne; Luetkens, Hubertus; Materne, Philipp; Klauss, Hans-Henning

2014-04-01

We present a detailed investigation of the electronic phase diagram of effectively charge compensated Ba1-xKx(Fe1-yCoy)2As2 with x /2≈y. Our experimental study by means of x-ray diffraction, Mössbauer spectroscopy, muon spin relaxation and ac-susceptibility measurements on polycrystalline samples is complemented by density functional electronic structure calculations. For low substitution levels of x /2≈y≤0.13, the system displays an orthorhombically distorted and antiferromagnetically ordered ground state. The low-temperature structural and magnetic order parameters are successively reduced with increasing substitution level. We observe a linear relationship between the structural and the magnetic order parameter as a function of temperature and substitution level for x /2≈y≤0.13. At intermediate substitution levels in the range between 0.13 and 0.19, we find superconductivity with a maximum Tc of 15 K coexisting with static magnetic order on a microscopic length scale. For higher substitution levels x /2≈y≥0.25, a tetragonal nonmagnetic ground state is observed. Our DFT calculations yield a significant reduction of the Fe 3d density of states at the Fermi energy and a strong suppression of the ordered magnetic moment in excellent agreement with experimental results. The appearance of superconductivity within the antiferromagnetic state can by explained by the introduction of disorder due to nonmagnetic impurities to a system with a constant charge carrier density.

Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duignan, Timothy T.; Baer, Marcel D.; Schenter, Gregory K.

Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for coarse grained models of electrolyte solution. Here, we provide rigorous definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation (DFT-MD) and isolate the effects of charge and cavitation,more » comparing to the Born (linear response) model. We show that using uncorrected Ewald summation leads to highly unphysical values for the solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small non-linearity for small anions. The charge hydration asymmetry (CHA) for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. This suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation. We would like to thank Thomas Beck, Shawn Kathmann, Richard Remsing and John Weeks for helpful discussions. Computing resources were generously allocated by PNNL's Institutional Computing program. This research also used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. TTD, GKS, and CJM were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. MDB was supported by MS3 (Materials Synthesis and Simulation Across Scales) Initiative, a Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national laboratory operated by Battelle for the U.S. Department of Energy.« less

Objective Molecular Dynamics with Self-consistent Charge Density Functional Tight-Binding (SCC-DFTB) Method

NASA Astrophysics Data System (ADS)

Dumitrica, Traian; Hourahine, Ben; Aradi, Balint; Frauenheim, Thomas

We discus the coupling of the objective boundary conditions into the SCC density functional-based tight binding code DFTB+. The implementation is enabled by a generalization to the helical case of the classical Ewald method, specifically by Ewald-like formulas that do not rely on a unit cell with translational symmetry. The robustness of the method in addressing complex hetero-nuclear nano- and bio-fibrous systems is demonstrated with illustrative simulations on a helical boron nitride nanotube, a screw dislocated zinc oxide nanowire, and an ideal double-strand DNA. Work supported by NSF CMMI 1332228.

DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid.

PubMed

Renuga Devi, T S; Sharmi kumar, J; Ramkumaar, G R

2015-02-25

The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm(-1) and 4000-50 cm(-1) respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee-Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic charges were calculated using both Hartee-Fock and density functional method using the cc-pVDZ basis set and compared. The calculated HOMO-LUMO energy gap revealed that charge transfer occurs within the molecule. (1)H and (13)C NMR chemical shifts of the molecule were calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The first order hyperpolarizability (β) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule. Copyright © 2014 Elsevier B.V. All rights reserved.

Charge injection in thin dielectric layers by atomic force microscopy: influence of geometry and material work function of the AFM tip on the injection process

NASA Astrophysics Data System (ADS)

Villeneuve-Faure, C.; Makasheva, K.; Boudou, L.; Teyssedre, G.

2016-06-01

Charge injection and retention in thin dielectric layers remain critical issues for the reliability of many electronic devices because of their association with a large number of failure mechanisms. To overcome this drawback, a deep understanding of the mechanisms leading to charge injection close to the injection area is needed. Even though the charge injection is extensively studied and reported in the literature to characterize the charge storage capability of dielectric materials, questions about charge injection mechanisms when using atomic force microscopy (AFM) remain open. In this paper, a thorough study of charge injection by using AFM in thin plasma-processed amorphous silicon oxynitride layers with properties close to that of thermal silica layers is presented. The study considers the impact of applied voltage polarity, work function of the AFM tip coating and tip curvature radius. A simple theoretical model was developed and used to analyze the obtained experimental results. The electric field distribution is computed as a function of tip geometry. The obtained experimental results highlight that after injection in the dielectric layer the charge lateral spreading is mainly controlled by the radial electric field component independently of the carrier polarity. The injected charge density is influenced by the nature of electrode metal coating (work function) and its geometry (tip curvature radius). The electron injection is mainly ruled by the Schottky injection barrier through the field electron emission mechanism enhanced by thermionic electron emission. The hole injection mechanism seems to differ from the electron one depending on the work function of the metal coating. Based on the performed analysis, it is suggested that for hole injection by AFM, pinning of the metal Fermi level with the metal-induced gap states in the studied silicon oxynitride layers starts playing a role in the injection mechanisms.

Effect of solid surface charge on the binding behaviour of a metal-binding peptide

PubMed Central

Donatan, Senem; Sarikaya, Mehmet; Tamerler, Candan; Urgen, Mustafa

2012-01-01

Over the last decade, solid-binding peptides have been increasingly used as molecular building blocks coupling bio- and nanotechnology. Despite considerable research being invested in this field, the effects of many surface-related parameters that define the binding of peptide to solids are still unknown. In the quest to control biological molecules at solid interfaces and, thereby, tailoring the binding characteristics of the peptides, the use of surface charge of the solid surface may probably play an important role, which then can be used as a potential tuning parameter of peptide adsorption. Here, we report quantitative investigation on the viscoelastic properties and binding kinetics of an engineered gold-binding peptide, 3RGBP1, adsorbed onto the gold surface at different surface charge densities. The experiments were performed in aqueous solutions using an electrochemical dissipative quartz crystal microbalance system. Hydrodynamic mass, hydration state and surface coverage of the adsorbed peptide films were determined as a function of surface charge density of the gold metal substrate. Under each charged condition, binding of 3rGBP1 displayed quantitative differences in terms of adsorbed peptide amount, surface coverage ratio and hydration state. Based on the intrinsically disordered structure of the peptide, we propose a possible mechanism for binding of the peptide that can be used for tuning surface adsorption in further studies. Controlled alteration of peptide binding on solid surfaces, as shown here, may provide novel methods for surface functionalization used for bioenabled processing and fabrication of future micro- and nanodevices. PMID:22491974

Effect of Dispersion on Surface Interactions of Cobalt(II) Octaethylporphyrin Monolayer on Au(111) and HOPG(0001) Substrates: a Comparative First Principles Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chilukuri, Bhaskar; Mazur, Ursula; Hipps, Kerry W.

A density functional theory study of a cobalt(II) octaethylporphyrin (CoOEP) monolayer on Au(111) and HOPG(0001) surfaces was performed under periodic boundary conditions. Calculations with and without dispersion corrections are performed and the effect of van der Waals forces on the interface properties is analyzed. Calculations have determined that the CoOEP molecule tends to bind at the 3-fold and the 6-fold center sites on Au(111) and HOPG(0001), respectively. Geometric optimizations at the center binding sites have indicated that the porphyrin molecules (in the monolayer) lie flat on both substrates. Calculations also reveal that the CoOEP monolayer binds slightly more strongly tomore » Au(111) than to HOPG(0001). Charge density difference plots disclose that charge is redistributed mostly around the porphyrin plane and the first layer of the substrates. Dispersion interactions cause a larger substrate to molecule charge pushback on Au(111) than on HOPG. CoOEP adsorption tends to lower the work functions of either substrate, qualitatively agreeing with the experimental photoelectron spectroscopic data. Comparison of the density of states (DOS) of the isolated CoOEP molecule with that on gold and HOPG substrates showed significant band shifts around the Fermi energy due to intermolecular orbital hybridization. Simulated STM images were plotted with the Tersoff–Hamann approach using the local density of states, which also agree with the experimental results. This study elucidates the role of dispersion for better describing porphyrin–substrate interactions. A DFT based overview of geometric, adsorption and electronic properties of a porphyrin monolayer on conductive surfaces is presented.« less

Effect of dispersion on surface interactions of cobalt(II) octaethylporphyrin monolayer on Au(111) and HOPG(0001) substrates: a comparative first principles study.

PubMed

Chilukuri, Bhaskar; Mazur, Ursula; Hipps, K W

2014-07-21

A density functional theory study of a cobalt(II) octaethylporphyrin (CoOEP) monolayer on Au(111) and HOPG(0001) surfaces was performed under periodic boundary conditions. Calculations with and without dispersion corrections are performed and the effect of van der Waals forces on the interface properties is analyzed. Calculations have determined that the CoOEP molecule tends to bind at the 3-fold and the 6-fold center sites on Au(111) and HOPG(0001), respectively. Geometric optimizations at the center binding sites have indicated that the porphyrin molecules (in the monolayer) lie flat on both substrates. Calculations also reveal that the CoOEP monolayer binds slightly more strongly to Au(111) than to HOPG(0001). Charge density difference plots disclose that charge is redistributed mostly around the porphyrin plane and the first layer of the substrates. Dispersion interactions cause a larger substrate to molecule charge pushback on Au(111) than on HOPG. CoOEP adsorption tends to lower the work functions of either substrate, qualitatively agreeing with the experimental photoelectron spectroscopic data. Comparison of the density of states (DOS) of the isolated CoOEP molecule with that on gold and HOPG substrates showed significant band shifts around the Fermi energy due to intermolecular orbital hybridization. Simulated STM images were plotted with the Tersoff-Hamann approach using the local density of states, which also agree with the experimental results. This study elucidates the role of dispersion for better describing porphyrin-substrate interactions. A DFT based overview of geometric, adsorption and electronic properties of a porphyrin monolayer on conductive surfaces is presented.

Charge-regularized swelling kinetics of polyelectrolyte gels: Elasticity and diffusion

NASA Astrophysics Data System (ADS)

Sen, Swati; Kundagrami, Arindam

2017-11-01

We apply a recently developed method [S. Sen and A. Kundagrami, J. Chem. Phys. 143, 224904 (2015)], using a phenomenological expression of osmotic stress, as a function of polymer and charge densities, hydrophobicity, and network elasticity for the swelling of spherical polyelectrolyte (PE) gels with fixed and variable charges in a salt-free solvent. This expression of stress is used in the equation of motion of swelling kinetics of spherical PE gels to numerically calculate the spatial profiles for the polymer and free ion densities at different time steps and the time evolution of the size of the gel. We compare the profiles of the same variables obtained from the classical linear theory of elasticity and quantitatively estimate the bulk modulus of the PE gel. Further, we obtain an analytical expression of the elastic modulus from the linearized expression of stress (in the small deformation limit). We find that the estimated bulk modulus of the PE gel decreases with the increase of its effective charge for a fixed degree of deformation during swelling. Finally, we match the gel-front locations with the experimental data, taken from the measurements of charged reversible addition-fragmentation chain transfer gels to show an increase in gel-size with charge and also match the same for PNIPAM (uncharged) and imidazolium-based (charged) minigels, which specifically confirms the decrease of the gel modulus value with the increase of the charge. The agreement between experimental and theoretical results confirms general diffusive behaviour for swelling of PE gels with a decreasing bulk modulus with increasing degree of ionization (charge). The new formalism captures large deformations as well with a significant variation of charge content of the gel. It is found that PE gels with large deformation but same initial size swell faster with a higher charge.

Heavy ion charge-state distribution effects on energy loss in plasmas.

PubMed

Barriga-Carrasco, Manuel D

2013-10-01

According to dielectric formalism, the energy loss of the heavy ion depends on its velocity and its charge density. Also, it depends on the target through its dielectric function; here the random phase approximation is used because it correctly describes fully ionized plasmas at any degeneracy. On the other hand, the Brandt-Kitagawa (BK) model is employed to depict the projectile charge space distribution, and the stripping criterion of Kreussler et al. is used to determine its mean charge state [Q]. This latter criterion implies that the mean charge state depends on the electron density and temperature of the plasma. Also, the initial charge state of the heavy ion is crucial for calculating [Q] inside the plasma. Comparing our models and estimations with experimental data, a very good agreement is found. It is noticed that the energy loss in plasmas is higher than that in the same cold gas cases, confirming the well-known enhanced plasma stopping (EPS). In this case, EPS is only due to the increase in projectile effective charge Q(eff), which is obtained as the ratio between the energy loss of each heavy ion and that of the proton in the same plasma conditions. The ratio between the effective charges in plasmas and in cold gases is higher than 1, but it is not as high as thought in the past. Finally, another significant issue is that the calculated effective charge in plasmas Q(eff) is greater than the mean charge state [Q], which is due to the incorporation of the BK charge distribution. When estimations are performed without this distribution, they do not fit well with experimental data.

Epitaxial growth and electronic properties of well ordered phthalocyanine heterojunctions MnPc/F{sub 16}CoPc

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindner, Susi; Mahns, Benjamin; Treske, Uwe

2014-09-07

We have prepared phthalocyanine heterojunctions out of MnPc and F{sub 16}CoPc, which were studied by means of X-ray absorption spectroscopy. This heterojunction is characterized by a charge transfer at the interface, resulting in charged MnPc{sup δ} {sup +} and F{sub 16}CoPc{sup δ} {sup −} species. Our data reveal that the molecules are well ordered and oriented parallel to the substrate surface. Furthermore, we demonstrate the filling of the Co 3d{sub z{sup 2}} orbital due to the charge transfer, which supports the explanation of the density functional theory, that the charge transfer is local and affects the metal centers only.

Doubly charged coronene clusters—Much smaller than previously observed

NASA Astrophysics Data System (ADS)

Mahmoodi-Darian, Masoomeh; Raggl, Stefan; Renzler, Michael; Goulart, Marcelo; Huber, Stefan E.; Mauracher, Andreas; Scheier, Paul; Echt, Olof

2018-05-01

The smallest doubly charged coronene cluster ions reported so far, Cor152+, were produced by charge exchange between bare coronene clusters and He2+ [H. A. B. Johansson et al., Phys. Rev. A 84, 043201 (2011)]. These dications are at least five times larger than the estimated Rayleigh limit, i.e., the size at which the activation barrier for charge separation vanishes. Such a large discrepancy is unheard of for doubly charged atomic or molecular clusters. Here we report the mass spectrometric observation of doubly charged coronene trimers, produced by electron ionization of helium nanodroplets doped with coronene. The observation implies that Cor32+ features a non-zero fission barrier too large to overcome under the present experimental conditions. The height of the barriers for the dimer and trimer has been estimated by means of density functional theory calculations. A sizeable barrier for the trimer has been revealed in agreement with the experimental findings.

Multiconfiguration pair-density functional theory investigation of the electronic spectrum of MnO4-

NASA Astrophysics Data System (ADS)

Sharma, Prachi; Truhlar, Donald G.; Gagliardi, Laura

2018-03-01

The electronic spectrum of permanganate ions contains various highly multiconfigurational ligand-to-metal charge transfer states and is notorious for being one of the most challenging systems to be treated by quantum-chemical methods. Here we studied the lowest nine vertical excitation energies using restricted active space second-order perturbation theory (RASPT2) and multiconfiguration pair-density functional theory (MC-PDFT) to test and compare these two theories in computing such a challenging spectrum. The results are compared to literature data, including time-dependent density functional theory, completely renormalized equation-of-motion couple-cluster theory with single and double excitations, symmetry-adapted-cluster configuration interaction, and experimental spectra in the gas phase and solution. Our results show that MC-PDFT accurately predicts the spectrum at a significantly reduced cost as compared to RASPT2.

Multiconfiguration pair-density functional theory investigation of the electronic spectrum of MnO4.

PubMed

Sharma, Prachi; Truhlar, Donald G; Gagliardi, Laura

2018-03-28

The electronic spectrum of permanganate ions contains various highly multiconfigurational ligand-to-metal charge transfer states and is notorious for being one of the most challenging systems to be treated by quantum-chemical methods. Here we studied the lowest nine vertical excitation energies using restricted active space second-order perturbation theory (RASPT2) and multiconfiguration pair-density functional theory (MC-PDFT) to test and compare these two theories in computing such a challenging spectrum. The results are compared to literature data, including time-dependent density functional theory, completely renormalized equation-of-motion couple-cluster theory with single and double excitations, symmetry-adapted-cluster configuration interaction, and experimental spectra in the gas phase and solution. Our results show that MC-PDFT accurately predicts the spectrum at a significantly reduced cost as compared to RASPT2.

Simple theoretical determination of the thickness of an alkali monolayer adsorbed on a jellium surface

NASA Astrophysics Data System (ADS)

Wojciechowski, K. F.; Rogowska, J. M.; Bogdanów, H.

1991-05-01

The thickness of a jellium slab representing an alkali monolayer on a jellium surface has been calculated, using parametrized trial functions for the electron density profile at the surface fulfilling the Budd-Vannimenus theorem and the charge neutrality condition. Reasonable values of the thicknesses of potassium, sodium, rubidium and caesium monolayers are obtained, which, contrary to earlier assumptions, depend on the bulk electron density of the substrate.

DOS cones along atomic chains

NASA Astrophysics Data System (ADS)

Kwapiński, Tomasz

2017-03-01

The electron transport properties of a linear atomic chain are studied theoretically within the tight-binding Hamiltonian and the Green’s function method. Variations of the local density of states (DOS) along the chain are investigated. They are crucial in scanning tunnelling experiments and give important insight into the electron transport mechanism and charge distribution inside chains. It is found that depending on the chain parity the local DOS at the Fermi level can form cone-like structures (DOS cones) along the chain. The general condition for the local DOS oscillations is obtained and the linear behaviour of the local density function is confirmed analytically. DOS cones are characterized by a linear decay towards the chain which is in contrast to the propagation properties of charge density waves, end states and Friedel oscillations in one-dimensional systems. We find that DOS cones can appear due to non-resonant electron transport, the spin-orbit scattering or for chains fabricated on a substrate with localized electrons. It is also shown that for imperfect chains (e.g. with a reduced coupling strength between two neighboring sites) a diamond-like structure of the local DOS along the chain appears.

In-flight calibration of mesospheric rocket plasma probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Havnes, Ove; University Studies Svalbard; Hartquist, Thomas W.

Many effects and factors can influence the efficiency of a rocket plasma probe. These include payload charging, solar illumination, rocket payload orientation and rotation, and dust impact induced secondary charge production. As a consequence, considerable uncertainties can arise in the determination of the effective cross sections of plasma probes and measured electron and ion densities. We present a new method for calibrating mesospheric rocket plasma probes and obtaining reliable measurements of plasma densities. This method can be used if a payload also carries a probe for measuring the dust charge density. It is based on that a dust probe's effectivemore » cross section for measuring the charged component of dust normally is nearly equal to its geometric cross section, and it involves the comparison of variations in the dust charge density measured with the dust detector to the corresponding current variations measured with the electron and/or ion probes. In cases in which the dust charge density is significantly smaller than the electron density, the relation between plasma and dust charge density variations can be simplified and used to infer the effective cross sections of the plasma probes. We illustrate the utility of the method by analysing the data from a specific rocket flight of a payload containing both dust and electron probes.« less

In-flight calibration of mesospheric rocket plasma probes.

PubMed

Havnes, Ove; Hartquist, Thomas W; Kassa, Meseret; Morfill, Gregor E

2011-07-01

Many effects and factors can influence the efficiency of a rocket plasma probe. These include payload charging, solar illumination, rocket payload orientation and rotation, and dust impact induced secondary charge production. As a consequence, considerable uncertainties can arise in the determination of the effective cross sections of plasma probes and measured electron and ion densities. We present a new method for calibrating mesospheric rocket plasma probes and obtaining reliable measurements of plasma densities. This method can be used if a payload also carries a probe for measuring the dust charge density. It is based on that a dust probe's effective cross section for measuring the charged component of dust normally is nearly equal to its geometric cross section, and it involves the comparison of variations in the dust charge density measured with the dust detector to the corresponding current variations measured with the electron and/or ion probes. In cases in which the dust charge density is significantly smaller than the electron density, the relation between plasma and dust charge density variations can be simplified and used to infer the effective cross sections of the plasma probes. We illustrate the utility of the method by analysing the data from a specific rocket flight of a payload containing both dust and electron probes.

GW-BSE approach on S1 vertical transition energy of large charge transfer compounds: A performance assessment.

PubMed

Ziaei, Vafa; Bredow, Thomas

2016-11-07

In this work, we apply many-body perturbation theory (MBPT) on large critical charge transfer (CT) complexes to assess its performance on the S 1 excitation energy. Since the S 1 energy of CT compounds is heavily dependent on the Hartree-Fock (HF) exchange fraction in the reference density functional, MBPT opens a new way for reliable prediction of CT S 1 energy without explicit knowledge of suitable amount of HF-exchange, in contrary to the time-dependent density functional theory (TD-DFT), where depending on various functionals, large errors can arise. Thus, simply by starting from a (semi-)local reference functional and performing update of Kohn-Sham (KS) energies in the Green's function G while keeping dynamical screened interaction (W(ω)) frozen to the mean-field level, we obtain impressingly highly accurate S 1 energy at slightly higher computational cost in comparison to TD-DFT. However, this energy-only updating mechanism in G fails to work if the initial guess contains a fraction or 100% HF-exchange, and hence considerably inaccurate S 1 energy is predicted. Furthermore, eigenvalue updating both in G and W(ω) overshoots the S 1 energy due to enhanced underscreening of W(ω), independent of the (hybrid-)DFT starting orbitals. A full energy-update on top of HF orbitals even further overestimates the S 1 energy. An additional update of KS wave functions within the Quasi-Particle Self-Consistent GW (QSGW) deteriorates results, in stark contrast to the good results obtained from QSGW for periodic systems. For the sake of transferability, we further present data of small critical non-charge transfer systems, confirming the outcomes of the CT-systems.

Controlling the Local Electronic Properties of Si(553)-Au through Hydrogen Doping

NASA Astrophysics Data System (ADS)

Hogan, C.; Speiser, E.; Chandola, S.; Suchkova, S.; Aulbach, J.; Schäfer, J.; Meyer, S.; Claessen, R.; Esser, N.

2018-04-01

We propose a quantitative and reversible method for tuning the charge localization of Au-stabilized stepped Si surfaces by site-specific hydrogenation. This is demonstrated for Si(553)-Au as a model system by combining density functional theory simulations and reflectance anisotropy spectroscopy experiments. We find that controlled H passivation is a two-step process: step-edge adsorption drives excess charge into the conducting metal chain "reservoir" and renders it insulating, while surplus H recovers metallic behavior. Our approach illustrates a route towards microscopic manipulation of the local surface charge distribution and establishes a reversible switch of site-specific chemical reactivity and magnetic properties on vicinal surfaces.

Fragmentation of amino acids induced by collisions with low-energy highly charged ions

NASA Astrophysics Data System (ADS)

Piekarski, D. G.; Maclot, S.; Domaracka, A.; Adoui, L.; Alcamí, M.; Rousseau, P.; Díaz-Tendero, S.; Huber, B. A.; Martín, F.

2014-04-01

Fragmentation of amino acids NH2-(CH2)n-COOH (n=1 glycine; n=2 β-alanine and n=3 γ-aminobutyric acid GABA) following collisions with slow highly charged ions has been studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multi-coincidence detection method was used to deduce the charge state of the molecules before fragmentation. Quantum chemistry calculations have been carried out in the basis of the density functional theory and ab initio molecular dynamics. The combination of both methodologies is essential to unambiguously unravel the different fragmentation pathways.

Ambipolar nature of dimethyl benzo difuran (DMBDF) molecule: A charge transport study

NASA Astrophysics Data System (ADS)

Sahoo, Smruti Ranjan; Sahu, Sridhar

2017-05-01

We describe a theoretical study of the charge transport properties of the organic dimethyl benzo difuran (DMBDF) molecule based on density functional theory (DFT). Reorganization energy, ionization potential (IP), electron affinity (EA), energy gaps, transfer integral (t) and charge mobility (μ) has been studied to depict the transport properties in the conjugated organic molecules. We computed, large homo transfer integral and IP value leading to high hole mobility (4.46 cm2/V sec). However, the electron reorganization energy (0.34 eV) and the electron mobility of 1.62 cm2/V sec, infers that the DMBDF organic molecule bears an ambipolar character.

Theoretical study on naphthobischalcogenadiazole conjugated polymer systems and C61 derivative as organic photovoltaic semiconductors

NASA Astrophysics Data System (ADS)

Fujita, Takehiro; Matsui, Toru; Sumita, Masato; Imamura, Yutaka; Morihashi, Kenji

2018-02-01

We investigated the charge-transfer reactions of solar cells including a quaterthiophene copolymer with naphtho-bis-thiadiazole (PNTz4T) and naphtho-bis-oxadiazole (PNOz4T) using constrained density functional theory (CDFT). According to our calculations, the high electron-transfer rate results in a highly efficient solar cell, and the stable charge-transfer state results in low energy loss. Our computations imply that the following three factors are crucial to improve the performance of semiconducting polymers: (i) large structural changes following charge-transfer, (ii) narrow band gap, and (iii) spatially delocalized lowest unoccupied molecular orbital (LUMO) of the ground state.

The tight binding model study of the role of anisotropic AFM spin ordering in the charge ordered CMR manganites

NASA Astrophysics Data System (ADS)

Kar, J. K.; Panda, Saswati; Rout, G. C.

2017-05-01

We propose here a tight binding model study of the interplay between charge and spin orderings in the CMR manganites taking anisotropic effect due to electron hoppings and spin exchanges. The Hamiltonian consists of the kinetic energies of eg and t2g electrons of manganese ion. It further includes double exchange and Heisenberg interactions. The charge density wave interaction (CDW) describes an extra mechanism for the insulating character of the system. The CDW gap and spin parameters are calculated using Zubarev's Green's function technique and computed self-consistently. The results are reported in this communication.

Ion temperatures in HIP-1 and SUMMA from charge-exchange neutral optical emission spectra

NASA Technical Reports Server (NTRS)

Patch, R. W.; Lauver, M. R.

1976-01-01

Ion temperatures were obtained from observations of the H sub alpha, D sub alpha, and He 587.6 nm lines emitted from hydrogen, deuterium, and helium plasmas in the SUMMA and HIP-1 mirror devices at Lewis Research Center. Steady state discharges were formed by applying a radially inward dc electric field between cylindrical or annular anodes and hollow cathodes located at the peaks of the mirrors. The ion temperatures were found from the Doppler broadening of the charge-exchange components of spectral lines. A statistical method was developed for obtaining scaling relations of ion temperature as a function of current, voltage, and magnetic flux density. Derivations are given that take into account triangular monochromator slit functions, loss cones, and superimposed charge-exchange processes. In addition, the Doppler broadening was found to be sensitive to the influence of drift on charge-exchange cross section. The effects of finite ion-cyclotron radius, cascading, and delayed emission are reviewed.

Oxygen vacancy effects in HfO2-based resistive switching memory: First principle study

NASA Astrophysics Data System (ADS)

Dai, Yuehua; Pan, Zhiyong; Wang, Feifei; Li, Xiaofeng

2016-08-01

The work investigated the shape and orientation of oxygen vacancy clusters in HfO2-base resistive random access memory (ReRAM) by using the first-principle method based on the density functional theory. Firstly, the formation energy of different local Vo clusters was calculated in four established orientation systems. Then, the optimized orientation and charger conductor shape were identified by comparing the isosurface plots of partial charge density, formation energy, and the highest isosurface value of oxygen vacancy. The calculated results revealed that the [010] orientation was the optimal migration path of Vo, and the shape of system D4 was the best charge conductor in HfO2, which effectively influenced the SET voltage, formation voltage and the ON/OFF ratio of the device. Afterwards, the PDOS of Hf near Vo and total density of states of the system D4_010 were obtained, revealing the composition of charge conductor was oxygen vacancy instead of metal Hf. Furthermore, the migration barriers of the Vo hopping between neighboring unit cells were calculated along four different orientations. The motion was proved along [010] orientation. The optimal circulation path for Vo migration in the HfO2 super-cell was obtained.

Floquet theory of microwave absorption by an impurity in the two-dimensional electron gas

NASA Astrophysics Data System (ADS)

Chepelianskii, Alexei D.; Shepelyansky, Dima L.

2018-03-01

We investigate the dynamics of a two-dimensional electron gas (2DEG) under circular polarized microwave radiation in the presence of dilute localized impurities. Inspired by recent developments on Floquet topological insulators we obtain the Floquet wave functions of this system which allow us to predict the microwave absorption and charge density responses of the electron gas; we demonstrate how these properties can be understood from the underlying semiclassical dynamics even for impurities with a size of around a magnetic length. The charge density response takes the form of a rotating charge density vortex around the impurity that can lead to a significant renormalization of the external microwave field which becomes strongly inhomogeneous on the scale of a cyclotron radius around the impurity. We show that this inhomogeneity can suppress the circular polarization dependence which is theoretically expected for microwave induced resistance oscillations but which was not observed in experiments on semiconducting 2DEGs. Our explanation for this so far unexplained polarization independence has close similarities with the Azbel'-Kaner effect in metals where the interaction length between the microwave field and conduction electrons is much smaller than the cyclotron radius due to skin effect generating harmonics of the cyclotron resonance.

Electron transport in doped fullerene molecular junctions

NASA Astrophysics Data System (ADS)

Kaur, Milanpreet; Sawhney, Ravinder Singh; Engles, Derick

The effect of doping on the electron transport of molecular junctions is analyzed in this paper. The doped fullerene molecules are stringed to two semi-infinite gold electrodes and analyzed at equilibrium and nonequilibrium conditions of these device configurations. The contemplation is done using nonequilibrium Green’s function (NEGF)-density functional theory (DFT) to evaluate its density of states (DOS), transmission coefficient, molecular orbitals, electron density, charge transfer, current, and conductance. We conclude from the elucidated results that Au-C16Li4-Au and Au-C16Ne4-Au devices behave as an ordinary p-n junction diode and a Zener diode, respectively. Moreover, these doped fullerene molecules do not lose their metallic nature when sandwiched between the pair of gold electrodes.

Molecular conformational analysis, vibrational spectra, NBO analysis and first hyperpolarizability of (2E)-3-(3-chlorophenyl)prop-2-enoic anhydride based on density functional theory calculations.

PubMed

Mary, Y Sheena; Raju, K; Panicker, C Yohannan; Al-Saadi, Abdulaziz A; Thiemann, Thies

2014-10-15

The conformational behavior and structural stability of (2E)-3-(3-chlorophenyl)prop-2-enoic anhydride were investigated by using density functional theory. The optimized molecular structure, vibrational wavenumbers, corresponding vibrational assignments of (2E)-3-(3-chlorophenyl)prop-2-enoic anhydride have been investigated experimentally and theoretically. The HOMO and LUMO analysis are used to determine the charge transfer within the molecule. The stability of the molecule arising from hyperconjugative interaction and charge delocalization has been analyzed using NBO analysis. The calculated first hyperpolarizability of the title compound is 15.8×10(-30)esu, and is 121.54 times that of the standard NLO material urea and the title compound is an attractive object for future studies of nonlinear optical properties. MEP was performed by the DFT method and the predicted infrared intensities and Raman activities have also been reported. Copyright © 2014 Elsevier B.V. All rights reserved.

Determinant quantum Monte Carlo study of the two-dimensional single-band Hubbard-Holstein model

DOE PAGES

Johnston, S.; Nowadnick, E. A.; Kung, Y. F.; ...

2013-06-24

Here, we performed numerical studies of the Hubbard-Holstein model in two dimensions using determinant quantum Monte Carlo (DQMC). We also present details of the method, emphasizing the treatment of the lattice degrees of freedom, and then study the filling and behavior of the fermion sign as a function of model parameters. We find a region of parameter space with large Holstein coupling where the fermion sign recovers despite large values of the Hubbard interaction. This indicates that studies of correlated polarons at finite carrier concentrations are likely accessible to DQMC simulations. We then restrict ourselves to the half-filled model andmore » examine the evolution of the antiferromagnetic structure factor, other metrics for antiferromagnetic and charge-density-wave order, and energetics of the electronic and lattice degrees of freedom as a function of electron-phonon coupling. From this we find further evidence for a competition between charge-density-wave and antiferromagnetic order at half- filling.« less

A model study of tunneling conductance spectra of ferromagnetically ordered manganites

NASA Astrophysics Data System (ADS)

Panda, Saswati; Kar, J. K.; Rout, G. C.

2018-02-01

We report here the interplay of ferromagnetism (FM) and charge density wave (CDW) in manganese oxide systems through the study of tunneling conductance spectra. The model Hamiltonian consists of strong Heisenberg coupling in core t2g band electrons within mean-field approximation giving rise to ferromagnetism. Ferromagnetism is induced in the itinerant eg electrons due to Kubo-Ohata type double exchange (DE) interaction among the t2g and eg electrons. The charge ordering (CO) present in the eg band giving rise to CDW interaction is considered as the extra-mechanism to explain the colossal magnetoresistance (CMR) property of manganites. The magnetic and CDW order parameters are calculated using Zubarev's Green's function technique and solved self-consistently and numerically. The eg electron density of states (DOS) calculated from the imaginary part of the Green's function explains the experimentally observed tunneling conductance spectra. The DOS graph exhibits a parabolic gap near the Fermi energy as observed in tunneling conductance spectra experiments.

Quantitative Analysis of the Efficiency of OLEDs.

PubMed

Sim, Bomi; Moon, Chang-Ki; Kim, Kwon-Hyeon; Kim, Jang-Joo

2016-12-07

We present a comprehensive model for the quantitative analysis of factors influencing the efficiency of organic light-emitting diodes (OLEDs) as a function of the current density. The model takes into account the contribution made by the charge carrier imbalance, quenching processes, and optical design loss of the device arising from various optical effects including the cavity structure, location and profile of the excitons, effective radiative quantum efficiency, and out-coupling efficiency. Quantitative analysis of the efficiency can be performed with an optical simulation using material parameters and experimental measurements of the exciton profile in the emission layer and the lifetime of the exciton as a function of the current density. This method was applied to three phosphorescent OLEDs based on a single host, mixed host, and exciplex-forming cohost. The three factors (charge carrier imbalance, quenching processes, and optical design loss) were influential in different ways, depending on the device. The proposed model can potentially be used to optimize OLED configurations on the basis of an analysis of the underlying physical processes.

Structure and Stability of GeAu{sub n}, n = 1-10 clusters: A Density Functional Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Priyanka,; Dharamvir, Keya; Sharma, Hitesh

2011-12-12

The structures of Germanium doped gold clusters GeAu{sub n} (n = 1-10) have been investigated using ab initio calculations based on density functional theory (DFT). We have obtained ground state geometries of GeAu{sub n} clusters and have it compared with Silicon doped gold clusters and pure gold clusters. The ground state geometries of the GeAu{sub n} clusters show patterns similar to silicon doped gold clusters except for n = 5, 6 and 9. The introduction of germanium atom increases the binding energy of gold clusters. The binding energy per atom of germanium doped cluster is smaller than the corresponding siliconmore » doped gold cluster. The HUMO-LOMO gap for Au{sub n}Ge clusters have been found to vary between 0.46 eV-2.09 eV. The mullikan charge analysis indicates that charge of order of 0.1e always transfers from germanium atom to gold atom.« less

Total-energy Assisted Tight-binding Method Based on Local Density Approximation of Density Functional Theory

NASA Astrophysics Data System (ADS)

Fujiwara, Takeo; Nishino, Shinya; Yamamoto, Susumu; Suzuki, Takashi; Ikeda, Minoru; Ohtani, Yasuaki

2018-06-01

A novel tight-binding method is developed, based on the extended Hückel approximation and charge self-consistency, with referring the band structure and the total energy of the local density approximation of the density functional theory. The parameters are so adjusted by computer that the result reproduces the band structure and the total energy, and the algorithm for determining parameters is established. The set of determined parameters is applicable to a variety of crystalline compounds and change of lattice constants, and, in other words, it is transferable. Examples are demonstrated for Si crystals of several crystalline structures varying lattice constants. Since the set of parameters is transferable, the present tight-binding method may be applicable also to molecular dynamics simulations of large-scale systems and long-time dynamical processes.

Ab Initio study on structural, electronic, magnetic and dielectric properties of LSNO within Density Functional Perturbation Theory

NASA Astrophysics Data System (ADS)

Petersen, John; Bechstedt, Friedhelm; Furthmüller, Jürgen; Scolfaro, Luisa

LSNO (La2-xSrxNiO4) is of great interest due to its colossal dielectric constant (CDC) and rich underlying physics. While being an antiferromagnetic insulator, localized holes are present in the form of stripes in the Ni-O planes which are commensurate with the inverse of the Sr concentration. The stripes are a manifestation of charge density waves with period approximately 1/x and spin density waves with period approximately 2/x. Here, the spin ground state is calculated via LSDA + U with the PAW method implemented in VASP. Crystal structure and the effective Hubbard U parameter are optimized before calculating ɛ∞ within the independent particle approximation. ɛ∞ and the full static dielectric constant (including the lattice polarizability) ɛ0 are calculated within Density Functional Perturbation Theory.

Experimental observation of charge-shift bond in fluorite CaF2.

PubMed

Stachowicz, Marcin; Malinska, Maura; Parafiniuk, Jan; Woźniak, Krzysztof

2017-08-01

On the basis of a multipole refinement of single-crystal X-ray diffraction data collected using an Ag source at 90 K to a resolution of 1.63 Å -1 , a quantitative experimental charge density distribution has been obtained for fluorite (CaF 2 ). The atoms-in-molecules integrated experimental charges for Ca 2+ and F - ions are +1.40 e and -0.70 e, respectively. The derived electron-density distribution, maximum electron-density paths, interaction lines and bond critical points along Ca 2+ ...F - and F - ...F - contacts revealed the character of these interactions. The Ca 2+ ...F - interaction is clearly a closed shell and ionic in character. However, the F - ...F - interaction has properties associated with the recently recognized type of interaction referred to as `charge-shift' bonding. This conclusion is supported by the topology of the electron localization function and analysis of the quantum theory of atoms in molecules and crystals topological parameters. The Ca 2+ ...F - bonded radii - measured as distances from the centre of the ion to the critical point - are 1.21 Å for the Ca 2+ cation and 1.15 Å for the F - anion. These values are in a good agreement with the corresponding Shannon ionic radii. The F - ...F - bond path and bond critical point is also found in the CaF 2 crystal structure. According to the quantum theory of atoms in molecules and crystals, this interaction is attractive in character. This is additionally supported by the topology of non-covalent interactions based on the reduced density gradient.

Light-front representation of chiral dynamics in peripheral transverse densities

DOE PAGES

Granados, Carlos G.; Weiss, Christian

2015-07-31

The nucleon's electromagnetic form factors are expressed in terms of the transverse densities of charge and magnetization at fixed light-front time. At peripheral transverse distances b = O(M_pi^{-1}) the densities are governed by chiral dynamics and can be calculated model-independently using chiral effective field theory (EFT). We represent the leading-order chiral EFT results for the peripheral transverse densities as overlap integrals of chiral light-front wave functions, describing the transition of the initial nucleon to soft pion-nucleon intermediate states and back. The new representation (a) explains the parametric order of the peripheral transverse densities; (b) establishes an inequality between the spin-independentmore » and -dependent densities; (c) exposes the role of pion orbital angular momentum in chiral dynamics; (d) reveals a large left-right asymmetry of the current in a transversely polarized nucleon and suggests a simple interpretation. The light-front representation enables a first-quantized, quantum-mechanical view of chiral dynamics that is fully relativistic and exactly equivalent to the second-quantized, field-theoretical formulation. It relates the charge and magnetization densities measured in low-energy elastic scattering to the generalized parton distributions probed in peripheral high-energy scattering processes. The method can be applied to nucleon form factors of other operators, e.g. the energy-momentum tensor.« less

Merely Measuring the UV-Visible Spectrum of Gold Nanoparticles Can Change Their Charge State.

PubMed

Navarrete, Jose; Siefe, Chris; Alcantar, Samuel; Belt, Michael; Stucky, Galen D; Moskovits, Martin

2018-02-14

Metallic nanostructures exhibit a strong plasmon resonance at a wavelength whose value is sensitive to the charge density in the nanostructure, its size, shape, interparticle coupling, and the dielectric properties of its surrounding medium. Here we use UV-visible transmission and reflectance spectroscopy to track the shifts of the plasmon resonance in an array of gold nanoparticles buried under metal-oxide layers of varying thickness produced using atomic layer deposition (ALD) and then coated with bulk layers of one of three metals: aluminum, silver, or gold. A significant shift in the plasmon resonance was observed and a precise value of ω p , the plasmon frequency of the gold comprising the nanoparticles, was determined by modeling the composite of gold nanoparticles and metal-oxide layer as an optically homogeneous film of core-shell particles bounded by two substrates: one of quartz and the other being one of the aforementioned metals, then using a Maxwell-Garnett effective medium expression to extract ω p for the gold nanoparticles before and after coating with the bulk metals. Under illumination, the change in the charge density of the gold nanoparticles per particle determined from the change in the values of ω p is found to be some 50-fold greater than what traditional electrostatic contact electrification models compute based on the work function difference of the two conductive materials. Moreover, when using bulk gold as the capping layer, which should have resulted in a negligible charge exchange between the gold nanoparticles and the bulk gold, a significant charge transfer from the bulk gold layer to the nanoparticles was observed as with the other metals. We explain these observations in terms of the "plasmoelectric effect", recently described by Atwater and co-workers, in which the gold nanoparticles modify their charge density to allow their resonant wavelength to match that of the incident light, thereby achieving, a lower value of the chemical potential due to the entropy increase resulting from the conversion of the plasmon's energy to heat. We conclude that even the act of registering the spectrum of nanoparticles is at times sufficient to alter their charge densities and hence their UV-visible spectra.

Compton profiles of NiO and TiO2 obtained from first principles GWA spectral function

NASA Astrophysics Data System (ADS)

S, M. Khidzir; M, F. M. Halid; W, A. T. Wan Abdullah

2016-06-01

In this work, we first use momentum density studies to understand strongly correlated electron behavior, which is typically seen in transition metal oxides. We observe that correlated electron behavior as seen in bulk NiO is due to the Fermi break located in the middle of overlapping spectral functions obtained from a GW (G is Green’s function and W is the screened Coulomb interaction) approximation (GWA) calculation while in the case of TiO2 we can see that the origin of the constant momentum distribution in lower momenta is due to a pile up of spectra before the Fermi energy. These observations are then used to compare our calculated Compton profiles with previous experimental studies of Fukamachi and Limandri. Our calculations for NiO are observed to follow the same trend as the experimental profile but it is seen to have a wide difference in the case of TiO2before the Fermi break. The ground state momentum densities differ significantly from the quasiparticle momentum density, thus stressing the importance of the quasiparticle wave function as the input for the study of charge density and the electron localization function. Finally we perform a calculation of the quasiparticle renormalization function, giving a quantitative description of the discontinuity of the GWA momentum density.

Charge density dependent mobility of organic hole-transporters and mesoporous TiO₂ determined by transient mobility spectroscopy: implications to dye-sensitized and organic solar cells.

PubMed

Leijtens, Tomas; Lim, Jongchul; Teuscher, Joël; Park, Taiho; Snaith, Henry J

2013-06-18

Transient mobility spectroscopy (TMS) is presented as a new tool to probe the charge carrier mobility of commonly employed organic and inorganic semiconductors over the relevant range of charge densities. The charge density dependence of the mobility of semiconductors used in hybrid and organic photovoltaics gives new insights into charge transport phenomena in solid state dye sensitized solar cells. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Numerical Simulations of Flow Separation Control in Low-Pressure Turbines using Plasma Actuators

NASA Technical Reports Server (NTRS)

Suzen, Y. B.; Huang, P. G.; Ashpis, D. E.

2007-01-01

A recently introduced phenomenological model to simulate flow control applications using plasma actuators has been further developed and improved in order to expand its use to complicated actuator geometries. The new modeling approach eliminates the requirement of an empirical charge density distribution shape by using the embedded electrode as a source for the charge density. The resulting model is validated against a flat plate experiment with quiescent environment. The modeling approach incorporates the effect of the plasma actuators on the external flow into Navier Stokes computations as a body force vector which is obtained as a product of the net charge density and the electric field. The model solves the Maxwell equation to obtain the electric field due to the applied AC voltage at the electrodes and an additional equation for the charge density distribution representing the plasma density. The new modeling approach solves the charge density equation in the computational domain assuming the embedded electrode as a source therefore automatically generating a charge density distribution on the surface exposed to the flow similar to that observed in the experiments without explicitly specifying an empirical distribution. The model is validated against a flat plate experiment with quiescent environment.